Self-cooling wafer polishing method

Abstract

The invention relates to a self-cooling wafer polishing method. The self-cooling wafer polishing method comprises the following steps: providing a wafer, wherein the Mohs hardness of the wafer is 8-10; fixing the wafer on a polishing pad by using a polishing head, wherein the polishing pad is made of a thermoplastic material; a polishing solution is guided into the side, making contact with the wafer, of the polishing pad through a polishing solution pipeline; the polishing solution does not contain grinding particles; and the polishing disc and the polishing head are rotated, and the wafer is subjected to the polishing process. According to the self-cooling wafer polishing method, self-cooling can be achieved in the polishing process, it is guaranteed that the temperature of the polishing pad is within a low range, the service life of the polishing pad can be effectively prolonged, the problems that a polishing head back film loses efficacy, and the polishing pad is degummed are solved, the wafer scratching risk is reduced, and the wafer polishing quality is improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductors, and in particular to a self-cooling wafer polishing method. Background Art

[0002] In the semiconductor manufacturing production process, the grinding unit of the CMP (chemical mechanical polishing) equipment mainly uses a grinding head to carry the wafer and give pressure to swing on the rotating grinding pad, accompanied by grinding liquid. The wafer is polished under the combined influence of chemical and mechanical effects to achieve comprehensive flatness. However, due to its ultra-high hardness (Mohs hardness 9.5), the silicon carbide (SiC) substrate wafer has a low polishing rate and often requires a larger downward pressure (5psi to 8psi, while conventional substrate polishing only requires 2psi to 4psi), a higher polishing disc (polishing pad) speed, and a longer operation time (tens of minutes to hours, while conventional thin film polishing only requires tens of seconds to minutes). This will undoubtedly cause the temperature of the polishing pad to continue to rise during continuous friction, which may lead to serious problems such as failure of the back film of the polishing head and debonding of the polishing pad. At the same time, it will increase the risk of scratches on the wafer surface and affect the processing quality. The same problem also exists for other materials with higher hardness (such as diamond, GaN, AlN, etc.) in the CMP process.

[0003] The methods for dealing with the high temperature of the polishing disk surface of the silicon carbide substrate in the prior art mainly include the following schemes: Scheme 1, increase the circulating cooling water under the polishing disk and lower the water temperature to take away the heat of the polishing disk. The problem with this scheme is that the efficiency is low, because the cooling water is far away from the polishing disk surface and the polishing pad. In order to improve the efficiency, the cooling water temperature needs to be continuously lowered, which undoubtedly increases the refrigeration cost, and the heat dissipation efficiency cannot be significantly improved; Scheme 2, reduce the polishing speed pressure and reduce the frictional heat generation, but this is undoubtedly not suitable for the high hardness characteristics of silicon carbide and cannot guarantee the processing efficiency; Scheme 3, increase the flow rate of the polishing liquid and use the excess polishing liquid to take away the heat of the polishing disk surface and the polishing pad. Although this method is direct and effective, it undoubtedly increases the amount of polishing liquid and increases the processing cost, which is often not accepted in actual industrial production.

[0004] Therefore, a self-cooling wafer polishing method is needed. For wafers with higher hardness such as silicon carbide, the temperature of the polishing pad can be reduced during the polishing process, thereby extending the service life of the polishing pad, avoiding problems such as failure of the polishing head back film and debonding of the polishing pad, and reducing the risk of wafer scratches. Summary of the invention

[0005] Therefore, the present invention provides a self-cooling wafer polishing method to solve the problem in the prior art that during the chemical mechanical polishing process of wafers with higher hardness, the polishing temperature is too high due to the low polishing rate, high polishing pressure and rotation speed, and long polishing time, which leads to failure of the polishing head back film, degumming of the polishing pad, and scratches on the wafer surface, thereby affecting the processing quality.

[0006] The present invention provides a self-cooling wafer polishing method, comprising:

[0007] Providing wafers, the Mohs hardness of the wafers is 8 to 10;

[0008] The wafer is fixed on the polishing pad by using the polishing head, and the material of the polishing pad is thermoplastic material;

[0009] The polishing liquid is introduced into the side of the polishing pad in contact with the wafer through the polishing liquid pipeline; the polishing liquid does not contain abrasive particles;

[0010] The polishing disc and polishing head are rotated to perform the polishing process on the wafer.

[0011] Optionally, during the polishing process, the polishing liquid chemically reacts with the wafer; the polishing pad physically grinds the wafer;

[0012] The temperature of the polishing pad is less than 55°C.

[0013] Optionally, the material of the wafer is SiC, GaN, AlN or diamond;

[0014] The polishing process takes more than 10 minutes.

[0015] Optionally, during the polishing process, polishing pressure is provided to the wafer via a pressurized gas path;

[0016] The polishing pressure is 6psi~9psi.

[0017] Optionally, the material of the wafer is SiC;

[0018] During the polishing process, the temperature of the polishing pad is less than or equal to 45°C.

[0019] Optionally, the thermal conductivity of the polishing pad is greater than 0.045 W / (m·K).

[0020] Optionally, the polishing pad is made of thermoplastic polyurethane.

[0021] Optionally, the polishing process has a polishing rate greater than 5 μm / h.

[0022] Optionally, the surface roughness of the wafer obtained after the polishing process is less than 0.1 nm.

[0023] Optionally, the step of performing a polishing process on the wafer further includes:

[0024] The temperature between the polishing pad and the wafer is measured in real time using a temperature measuring device.

[0025] The technical solution of the present invention has the following advantages:

[0026] (1) The self-cooling wafer polishing method provided by the present invention uses a polishing liquid without abrasive particles, which can reduce the friction between the polishing pad and the wafer and control the temperature of the polishing pad from being too high; at the same time, the polishing pad made of thermoplastic material can generate relatively low heat during continuous friction by utilizing its flexible thermal deformation effect and good thermal conductivity, so that the polishing pad maintains a low temperature and realizes self-cooling of the polishing pad during the polishing process. The self-cooling wafer polishing method provided by the present invention can realize self-cooling during the polishing process, ensure that the temperature of the polishing pad is within a relatively low range, effectively extend the service life of the polishing pad, avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad, reduce the risk of wafer scratches, and improve the quality of wafer polishing.

[0027] (2) In the self-cooling wafer polishing method provided by the present invention, the polishing liquid and the wafer undergo a chemical reaction to achieve the purpose of polishing. The physical grinding of the wafer by the polishing pad can trim the wafer surface and remove excess grinding liquid, effectively avoiding heat generated by mechanical friction between the grinding particles and the polishing pad, making the polishing pad temperature less than 55°C, and avoiding problems such as failure of the polishing head back film and debonding of the polishing pad. At the same time, the polishing liquid does not contain grinding particles, which also reduces the risk of wafer scratches and improves the wafer polishing quality.

[0028] (3) In the self-cooling wafer polishing method provided by the present invention, for SiC wafers, a polishing pad made of thermoplastic material and a polishing liquid without abrasive particles are used to perform a polishing process, which can achieve self-cooling of the polishing pad and keep the temperature of the polishing pad less than or equal to 45°C. Even if the polishing process time is greater than 10 minutes, the temperature of the polishing pad will not rise any more, which can effectively extend the service life of the polishing pad, avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad, reduce the risk of wafer scratches, and improve the wafer polishing quality.

[0029] (4) The self-cooling wafer polishing method provided by the present invention has a surface roughness of less than 0.1 nmh after the polishing process, which can ensure the polishing effect of the wafer. At the same time, the self-cooling of the polishing pad can be achieved during the polishing process, and the temperature of the polishing pad can be kept within a relatively low range. The service life of the polishing pad can be effectively extended, and problems such as failure of the back film of the polishing head and debonding of the polishing pad can be avoided, thereby reducing the risk of wafer scratches and improving the quality of wafer polishing.

[0030] (5) The self-cooling wafer polishing method provided by the present invention has a surface roughness of less than 0.1 nm after the polishing process, which can ensure the polishing effect of the wafer. At the same time, the self-cooling of the polishing pad can be achieved during the polishing process, and the temperature of the polishing pad can be kept within a relatively low range. The service life of the polishing pad can be effectively extended, and problems such as failure of the back film of the polishing head and debonding of the polishing pad can be avoided, thereby reducing the risk of wafer scratches and improving the quality of wafer polishing.

[0031] (6) The self-cooling wafer polishing method provided by the present invention can ensure that the polishing rate of the wafer and the surface roughness of the wafer after polishing are at the same level compared with the conventional process, thereby ensuring the polishing effect of the wafer. On the one hand, by selecting a polishing pad made of thermoplastic polyurethane material, the flexible thermal deformation effect and good thermal conductivity of the polishing pad can be used to generate relatively low heat in continuous friction, thereby ensuring that the polishing pad can achieve self-cooling in the polishing process. Under the same conditions, the polishing pad temperature is 7°C lower than that of the polishing pad made of thermosetting material; on the other hand, by selecting a polishing liquid without abrasive particles, the friction between the polishing pad and the wafer can be reduced to prevent the wafer surface from being scratched, and the polishing pad temperature can be further controlled not to be too high. Under the same conditions, the polishing pad temperature is further reduced by 3°C than that of the polishing pad in the polishing liquid process containing 2wt% abrasive particles; finally, the self-cooling of the polishing pad temperature can be achieved. Compared with the conventional polishing process, the polishing pad temperature is reduced by 10°C, ensuring that the polishing pad temperature is within a relatively low range, which can effectively extend the service life of the polishing pad, avoid the problems of polishing head back film failure and polishing pad debonding, and also reduce the risk of wafer scratches and improve the wafer polishing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A schematic flow chart of a self-cooling wafer polishing method according to an embodiment of the present invention;

[0034] Figure 2 A schematic diagram of the structure of a CMP device according to an embodiment of the present invention;

[0035] Figure 3 A schematic diagram of the structure of another CMP device according to an embodiment of the present invention;

[0036] Figure 4 The present invention is a schematic diagram of a specific process of a self-cooling wafer polishing method according to an embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of a specific process of a self-cooling wafer polishing method for comparative example 1.

[0038] Description of reference numerals:

[0039] 10-polishing disc; 20-polishing pad; 30-polishing head; 40-polishing liquid pipeline; 50-pressure gas line; 60-temperature measuring device; 100-wafer. DETAILED DESCRIPTION

[0040] At present, the CMP process for wafers with Mohs hardness greater than or equal to 8 (such as diamond, GaN, AlN, SiC, etc.) has the problem of excessive polishing pad temperature affecting equipment quality and polishing effect. In particular, due to its high hardness characteristics (Mohs hardness 9.5. Diamond 10), efficient and high-quality grinding and polishing of silicon carbide wafers has always been a major technical difficulty. In order to cope with its ultra-high hardness, it is often necessary to apply a large pressure (5psi to 8psi, compared with only 2psi to 4psi for conventional thin-film polishing) and continue the operation for a long time (tens of minutes to hours, compared with only tens of seconds to minutes for conventional thin-film polishing). Therefore, it is inevitable that the temperature of the polishing disk and wafer will continue to rise during the continuous friction process. Excessive temperature may cause serious problems such as failure of the back film of the polishing head and debonding of the polishing pad, and also increase the risk of scratches on the wafer surface, affecting the processing quality.

[0041] Common methods for reducing the disk surface temperature during polishing include connecting a circulating cooling water line under the polishing disk, reducing the rotation speed, pressure and other frictional heat generating conditions, increasing the polishing liquid flow rate, etc. These methods are not practical or effective enough in silicon carbide polishing. Therefore, starting from the perspective of the selection of polishing liquid and polishing pad, the cooling effect can be further improved and the adverse effects of other methods on polishing efficiency and cost can be reduced.

[0042] In order to solve the problem in the prior art that a wafer with a relatively high hardness has a high polishing temperature due to a low polishing rate, a high polishing pressure and a high rotation speed, and a long polishing time during a chemical mechanical polishing process, which leads to failure of a back film of a polishing head, debonding of a polishing pad, and scratches on the surface of the wafer, thereby affecting the processing quality, the present invention provides a self-cooling wafer polishing method, comprising: providing a wafer, wherein the Mohs hardness of the wafer is 8 to 10; fixing the wafer on a polishing pad using a polishing head, wherein the material of the polishing pad is a thermoplastic material; introducing a polishing liquid into a side of the polishing pad in contact with the wafer through a polishing liquid pipeline; the polishing liquid does not contain abrasive particles; and rotating a polishing disk and a polishing head to perform a polishing process on the wafer.

[0043] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In the description of the present invention, it should be noted that the terms "first", "second" and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment provides a self-cooling wafer polishing method, comprising:

[0046] S101, providing a wafer, wherein the Mohs hardness of the wafer is 8 to 10.

[0047] In a specific implementation, the wafer may be silicon carbide (Mohs hardness is 9.5), GaN (Mohs hardness is 9.5), AlN (Mohs hardness is 7-8), etc.

[0048] S102, using a polishing head to fix the wafer on a polishing pad, the polishing pad being made of a thermoplastic material.

[0049] In specific implementation, thermoplastic material is a material that can be shaped when heated and retains its shape after cooling. This material can adjust its shape by repeated heating and shaping, because they soften when heated and harden when cooled. Compared with the polishing pad of traditional thermosetting material, its micro-deformation and reshaping after heating make it have better thermal conductivity, and heat is not easy to accumulate during friction, so it has a lower temperature and can achieve self-cooling in the polishing process. Specifically, the material of the polishing pad can be thermoplastic polyurethane, thermoplastic polyurethane, etc.

[0050] S103, introducing the polishing liquid to the side of the polishing pad in contact with the wafer through the polishing liquid pipeline; the polishing liquid does not contain abrasive particles.

[0051] Conventional polishing liquids are added with abrasive particles (usually 2wt% to 20wt% of powdered abrasive particles) to mechanically rub against the wafer during the polishing process to achieve the removal effect. However, for wafers with a Mohs hardness of 8 to 10, the removal efficiency of common abrasive particles on the wafer is very low and almost ineffective. Instead, the mechanical friction between the wafer, abrasive particles and polishing pad generates heat, causing the temperature of the polishing pad to rise significantly. Therefore, conventional polishing liquids cannot achieve the purpose of polishing. Therefore, the present embodiment selects a polishing liquid without abrasive particles, which can reduce the friction between the polishing pad and the wafer, avoid a significant increase in the temperature of the polishing pad, and will not affect the polishing rate.

[0052] S104, rotating the polishing plate and the polishing head to perform a polishing process on the wafer.

[0053] In specific implementation, in the polishing process, since the polishing pad made of thermoplastic material has good thermal conductivity, heat is not easy to accumulate during the polishing process, which can ensure that the polishing pad maintains a low temperature and achieve self-cooling in the polishing process; at the same time, since the polishing liquid does not contain abrasive particles, the friction between the polishing pad and the wafer can be reduced, and the temperature of the polishing pad is controlled not to be too high.

[0054] The self-cooling wafer polishing method provided by the present embodiment uses a polishing liquid without abrasive particles, which can reduce the friction between the polishing pad and the wafer and control the temperature of the polishing pad from being too high; at the same time, a polishing pad made of thermoplastic material can generate relatively low heat in continuous friction by utilizing its flexible thermal deformation effect and good thermal conductivity, thereby ensuring that the polishing pad maintains a low temperature and realizing self-cooling in the polishing process. The self-cooling wafer polishing method provided by the present invention can realize self-cooling in the polishing process, ensuring that the temperature of the polishing pad is within a relatively low range, effectively extending the service life of the polishing pad, avoiding problems such as failure of the back film of the polishing head and debonding of the polishing pad, reducing the risk of wafer scratches, and improving the quality of wafer polishing.

[0055] The self-cooling wafer polishing method provided in this embodiment is to polish the wafer 100 by using a CMP device.

[0056] like Figure 2 As shown, the CMP equipment includes:

[0057] Polishing disc 10;

[0058] A polishing pad 20, located on one side of the polishing plate 10;

[0059] The polishing head 30 is located on the side of the polishing pad 20 facing away from the polishing plate 10 and is arranged opposite to the polishing pad 20. The polishing head 30 is used to fix the wafer 100;

[0060] A polishing liquid pipeline 40 is located on the side of the polishing pad 20 facing away from the polishing plate 10, and the polishing liquid pipeline 40 is used to provide polishing liquid;

[0061] The pressure gas circuit 50 is located on the side of the polishing head 30 facing away from the polishing pad 20 , and is used to provide polishing pressure.

[0062] The main components of the CMP equipment include a polishing head 30 and a polishing disc 10, on which a polishing pad 20 is attached. During the polishing process, the polishing head 30 sucks the back of the wafer 100 to be polished and presses the front of the wafer 100 on the surface of the polishing pad 20, and the polishing head 30 and the polishing disc 10 rotate to perform polishing. During the chemical mechanical polishing process, the polishing liquid is provided between the polishing pad 20 and the wafer 100 through the polishing liquid pipeline 40, and the polishing rate is adjusted by adjusting the pressure of the polishing head through the pressure gas circuit 50. The rotation speed of the polishing disc is 100rpm~150rpm, and the rotation speed of the polishing head is 100rpm~150rpm.

[0063] Further, in some embodiments, during the polishing process, the polishing liquid chemically reacts with the wafer; the polishing pad physically grinds the wafer;

[0064] The temperature of the polishing pad is less than 55°C, such as 54°C, 52°C, 48°C, or 45°C.

[0065] In the existing polishing process, a polishing liquid with abrasive particles is used, and the abrasive particles physically grind the wafer to polish the wafer surface to achieve the removal effect. However, this process will cause the temperature of the polishing pad to rise significantly, and the polishing pad will be greater than or equal to 55°C, resulting in failure of the back film of the polishing head and debonding of the polishing pad. In this solution, the polishing liquid and the wafer undergo a strong chemical reaction to achieve the purpose of polishing, and the physical grinding of the wafer by the polishing pad is only to trim the wafer surface and remove excess abrasive liquid. Compared with the existing technology, the friction between the abrasive particles and the wafer and the polishing pad is reduced, and the temperature of the polishing pad is less than 55°C.

[0066] In the self-cooling wafer polishing method provided in this embodiment, the polishing liquid and the wafer undergo a chemical reaction to achieve the purpose of polishing. The physical grinding of the wafer by the polishing pad can trim the wafer surface and remove excess grinding liquid, effectively avoiding heat generated by mechanical friction between the grinding particles and the polishing pad, making the polishing pad temperature less than 55°C, and avoiding problems such as failure of the polishing head back film and debonding of the polishing pad. At the same time, the fact that the polishing liquid does not contain grinding particles also reduces the risk of wafer scratches and improves the wafer polishing quality.

[0067] Further, in some embodiments, the material of the wafer is SiC, GaN, AlN or diamond;

[0068] The polishing process may take longer than 10 minutes, such as 10 minutes, 30 minutes, 60 minutes or 120 minutes.

[0069] In specific implementation, in some embodiments, the material of the wafer is SiC, GaN, AlN or diamond, and the Mohs hardness of these materials is relatively high, and the polishing process time is greater than 10 minutes, and may even reach several hours. Therefore, the long polishing process will cause the mechanical friction between the wafer and the polishing pad to generate high heat. By using a polishing pad made of thermoplastic material, it can generate relatively low heat in continuous friction by utilizing its flexible thermal deformation effect and good thermal conductivity. At the same time, using a polishing liquid without abrasive particles can reduce the friction between the polishing pad and the wafer, thereby keeping the polishing pad at a low temperature.

[0070] Further, in some embodiments, during the polishing process, polishing pressure is provided to the wafer via a pressurized gas path;

[0071] The polishing pressure is 6 psi to 9 psi, such as 6 psi, 7 psi, 8 psi or 9 psi.

[0072] In the prior art, the conventional CMP process polishing pressure is generally 2psi~4psi, while in this embodiment, due to the high hardness of the wafer, the polishing pressure is 6psi~9psi, which will cause the mechanical friction between the wafer and the polishing pad to generate high heat. By using a polishing pad made of thermoplastic material, its flexible thermal deformation effect and good thermal conductivity can generate relatively low heat in continuous friction. At the same time, using a polishing liquid that does not contain abrasive particles can reduce the friction between the polishing pad and the wafer, thereby keeping the polishing pad at a low temperature.

[0073] Further, in some embodiments, the material of the wafer is SiC;

[0074] During the polishing process, the temperature of the polishing pad is less than or equal to 45°C.

[0075] In specific implementation, for SiC wafers, a polishing process is carried out using a polishing pad made of thermoplastic material and a polishing liquid without abrasive particles. This can achieve self-cooling of the polishing pad and keep the temperature of the polishing pad less than or equal to 45°C. Even if the polishing process time is greater than 10 minutes, the temperature of the polishing pad will not rise any more. This can effectively extend the service life of the polishing pad, avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad, reduce the risk of wafer scratches, and improve the wafer polishing quality.

[0076] Furthermore, in some embodiments, the thermal conductivity of the polishing pad is greater than 0.045 W / (m·K).

[0077] In specific implementation, the thermal conductivity of the polishing pad is greater than 0.045W / (m·k), which is higher than that of traditional polishing pads made of thermosetting materials. At the same time, the flexible thermal deformation effect of thermoplastic materials can be used to dissipate heat, thereby ensuring that the polishing pad can generate relatively low heat during continuous friction, so that the polishing pad maintains a low temperature and achieves self-cooling of the polishing pad during the polishing process, thereby extending the service life of the polishing pad and avoiding problems such as failure of the back film of the polishing head and debonding of the polishing pad.

[0078] Furthermore, in some embodiments, the polishing pad is made of thermoplastic polyurethane.

[0079] Thermoplastic polyurethane is a common thermoplastic material with many excellent properties. For example, thermoplastic polyurethane has good elasticity and toughness, and can adapt to materials of different shapes and surfaces during the polishing process, thereby improving the polishing effect; thermoplastic polyurethane has strong wear resistance, can maintain a long service life under high-intensity use, and reduce the frequency and cost of replacement. Thermoplastic polyurethane has good tolerance to a variety of chemical substances, can be used in a variety of polishing agents and cleaning agents, and has a wide range of applications; the low density and light weight of thermoplastic polyurethane can make the polishing pad easy to operate and improve work efficiency; thermoplastic polyurethane also has good processability, and can be made into polishing pads of different shapes and sizes through a variety of processing methods (such as thermoforming, injection molding, etc.) to meet different application requirements. Therefore, thermoplastic polyurethane has good elasticity, wear resistance and chemical corrosion resistance. Using it as a polishing pad can make the thermoplastic polyurethane polishing pad maintain a long service life while being able to effectively adapt to the polishing needs of various complex surfaces.

[0080] At the same time, thermoplastic polyurethane has flexible thermal deformation effect and good thermal conductivity, which can generate relatively low heat during the friction between the polishing pad and the wafer, so that the polishing pad maintains a low temperature and realizes self-cooling of the polishing pad during the polishing process. Keeping the temperature of the polishing pad within a low range can effectively extend the service life of the polishing pad and avoid problems such as failure of the back film of the polishing head and degumming of the polishing pad.

[0081] Furthermore, in some embodiments, the polishing process has a polishing rate greater than 5 μm / h.

[0082] The self-cooling wafer polishing method provided in this embodiment has a polishing rate of more than 5 μm / h in the polishing process, which can ensure the polishing effect of the wafer. At the same time, the self-cooling of the polishing pad can be achieved in the polishing process, and the temperature of the polishing pad can be kept within a relatively low range, which can effectively extend the service life of the polishing pad, avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad, reduce the risk of wafer scratches, and improve the quality of wafer polishing.

[0083] Furthermore, in some embodiments, the surface roughness of the wafer obtained after the polishing process is less than 0.1 nm.

[0084] The self-cooling wafer polishing method provided in this embodiment has a surface roughness of less than 0.1 nm for the wafer obtained after the polishing process, which can ensure the polishing effect of the wafer. At the same time, the self-cooling of the polishing pad can be achieved during the polishing process, and the temperature of the polishing pad can be kept within a relatively low range, which can effectively extend the service life of the polishing pad, avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad, reduce the risk of wafer scratches, and improve the quality of wafer polishing.

[0085] Furthermore, in some embodiments, the step of performing a polishing process on the wafer further includes:

[0086] The temperature between the polishing pad and the wafer is measured in real time using a temperature measuring device.

[0087] like Figure 3 As shown, the CMP equipment further includes: a temperature measuring device 60 , which is disposed on the polishing head. During the polishing process, the temperature between the polishing pad 20 and the wafer 100 is measured in real time by the temperature measuring device 60 .

[0088] In a specific embodiment, Example 1 provides a specific process of a self-cooling wafer polishing method, referring to Figure 4 , including steps S201-S204:

[0089] S201, provide a silicon carbide wafer.

[0090] S202, using a polishing head to fix the wafer on a polishing pad, the material of the polishing pad is thermoplastic polyurethane.

[0091] S203, introducing the polishing liquid to the side of the polishing pad in contact with the wafer through the polishing liquid pipeline; the polishing liquid does not contain abrasive particles.

[0092] S204, rotating the polishing disc and the polishing head, performing a polishing process on the wafer, and measuring the temperature between the polishing pad and the wafer in real time; the polishing pressure is 6psi to 9psi, and the polishing process time is greater than 10 minutes.

[0093] In order to verify the effectiveness of the solution of this embodiment, this embodiment also provides a comparative example 1, such as Figure 5As shown, it includes steps S301-S304. The difference between Comparative Example 1 and the above Example 1 is that: the material of the polishing pad in step S302 is a thermosetting material; the polishing liquid in step S304 contains 2wt% abrasive particles. The remaining steps are the same as those in the above Example 1. After testing, the comparison of the polishing effect and temperature effect in the polishing process of Example 1 and the polishing effect and temperature effect in the polishing process of Comparative Example 1 is shown in Table 1. It can be seen that the polishing effect and temperature effect of the self-cooling wafer polishing method provided in Example 1 in this embodiment are better than those in Comparative Example 1.

[0094] Table 1: Comparison of polishing effect and temperature effect between Example 1 and Comparative Example 1

[0095] Comparative Example 1 Example 1 Polishing rate >5μm / h >5μm / h Scratch level Minor shallow scratches No scratches Wafer surface roughness <0.1nm <0.1nm Polishing disk temperature 55℃ 45℃

[0096] It can be seen from the table that compared with comparative example 1, the polishing rate and the surface roughness of the wafer after polishing of example 1 are maintained at the same level, but example 1 will not scratch the wafer surface, and the polishing pad temperature is 45°C, which is 10°C lower than comparative example 1. It can be proved that the self-cooling wafer polishing method provided by example 1 can ensure that the polishing rate of the wafer is greater than 5μm / h and the surface roughness of the wafer after polishing is less than 1nm, and at the same time, self-cooling can be achieved in the polishing process to ensure that the polishing pad temperature is less than or equal to 45°C, which can effectively extend the service life of the polishing pad, avoid the problems of polishing head back film failure, polishing pad debonding, etc., reduce the risk of wafer scratches, and improve the quality of wafer polishing.

[0097] In addition, in order to verify the self-cooling effect of the polishing pad made of thermoplastic material, the present invention also provides Comparative Example 2, which is different from Comparative Example 1 in that the material of the polishing pad is thermoplastic polyurethane. The remaining steps are the same as those of Comparative Example 1. After testing, the comparison of the polishing effect and temperature effect in the polishing process of Comparative Example 1 and the polishing effect and temperature effect in the polishing process of Comparative Example 2 is shown in Table 2.

[0098] Table 2: Comparison of polishing effect and temperature effect between comparative example 1 and comparative example 2

[0099] Comparative Example 1 Comparative Example 2 Polishing rate >5μm / h >5μm / h Polishing disk temperature 55℃ 48℃

[0100] It can be seen from the table that the polishing rate of Comparative Example 2 is the same as that of Comparative Example 1, both of which are greater than 5 μm / h; and the polishing pad temperature of Comparative Example 2 is 48°C, which is 7°C lower than that of Comparative Example 1. This proves that by selecting a polishing pad made of thermoplastic polyurethane material, the polishing rate of the wafer can be guaranteed to be greater than 5 μm / h, and at the same time, the polishing pad can achieve self-cooling during the polishing process, ensuring that the polishing pad temperature is less than or equal to 48°C, which can effectively extend the service life of the polishing pad and avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad.

[0101] Finally, in order to verify the self-cooling effect of the polishing liquid without abrasive particles, the present invention also provides a comparative example 3, which is different from the comparative example 1 in that the polishing liquid does not contain abrasive particles. The remaining steps are the same as the comparative example 1. After testing, the comparison of the polishing effect and temperature effect in the polishing process of comparative example 1 and the polishing effect and temperature effect in the polishing process of comparative example 3 is shown in Table 3.

[0102] Table 3: Comparison of polishing effect and temperature effect between comparative example 1 and comparative example 3

[0103] Comparative Example 1 Comparative Example 3 Polishing rate >5μm / h >5μm / h Scratch level Minor shallow scratches No scratches Wafer surface roughness <0.1nm <0.1nm Polishing disk temperature 55℃ 52℃

[0104] As can be seen from the table, compared with Comparative Example 1, the polishing rate and the surface roughness of the wafer after polishing of Comparative Example 3 are maintained at the same level, but Comparative Example 3 does not cause scratches on the wafer surface, and the polishing pad temperature is 52°C, which is 3°C lower than that of Comparative Example 1. It can be proved that by using a polishing liquid without abrasive particles, the polishing rate of the wafer can be guaranteed to be greater than 5μm / h and the surface roughness of the wafer after polishing can be less than 1nm, and at the same time, the polishing pad can achieve self-cooling in the polishing process, ensuring that the polishing pad temperature is less than or equal to 52°C, which can extend the service life of the polishing pad, avoid problems such as failure of the back film of the polishing head and debonding of the polishing pad, and reduce the risk of wafer scratches, thereby improving the quality of wafer polishing.

[0105] In summary, through comparative analysis of Example 1 and Comparative Examples 1 to 3, the self-cooling wafer polishing method provided in this embodiment can ensure that the polishing rate of the wafer and the surface roughness of the wafer after polishing are at the same level, thereby ensuring the polishing effect of the wafer, compared with the conventional process. On the one hand, by selecting a polishing pad made of thermoplastic polyurethane material and utilizing its flexible thermal deformation effect and good thermal conductivity, relatively low heat can be generated in continuous friction, ensuring that the polishing pad can achieve self-cooling during the polishing process. Under the same conditions, the polishing pad temperature is 7°C lower than that of a polishing pad made of thermosetting material. On the other hand, by selecting a polishing liquid that does not contain abrasive particles, the friction between the polishing pad and the wafer can be reduced to prevent scratches on the wafer surface. At the same time, the polishing pad temperature can be further controlled not to be too high. Under the same conditions, the polishing pad temperature is further reduced by 3°C than the polishing pad temperature in the polishing liquid process containing 2wt% abrasive particles. Finally, self-cooling of the polishing pad temperature can be achieved. Compared with conventional polishing processes, the polishing pad temperature is reduced by 10°C, ensuring that the polishing pad temperature is within a lower range, which can effectively extend the service life of the polishing pad and avoid problems such as failure of the polishing head back film and debonding of the polishing pad. At the same time, the risk of wafer scratches is reduced and the wafer polishing quality is improved.

[0106] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A self-cooling wafer polishing method, characterized in that: include: Providing a wafer, wherein the Mohs hardness of the wafer is 8 to 10; The wafer is fixed on a polishing pad using a polishing head, wherein the polishing pad is made of a thermoplastic material; Introducing the polishing liquid to the side of the polishing pad in contact with the wafer through a polishing liquid pipeline; the polishing liquid does not contain abrasive particles; The polishing plate and the polishing head are rotated to perform a polishing process on the wafer.

2. The self-cooling wafer polishing method according to claim 1, characterized in that: In the polishing process, the polishing liquid reacts chemically with the wafer; the polishing pad physically grinds the wafer; The polishing pad has a temperature less than 55°C.

3. The self-cooling wafer polishing method according to claim 1, characterized in that: The material of the wafer is SiC, GaN, AlN or diamond; The polishing process takes longer than 10 minutes.

4. The self-cooling wafer polishing method according to claim 3, characterized in that: In the polishing process, polishing pressure is provided to the wafer through a pressurized gas path; The polishing pressure is 6 psi to 9 psi.

5. The self-cooling wafer polishing method according to claim 4, characterized in that: The material of the wafer is SiC; In the polishing process, the temperature of the polishing pad is less than or equal to 45°C.

6. The self-cooling wafer polishing method according to claim 1, characterized in that: The thermal conductivity of the polishing pad is greater than 0.045 W / (m·k).

7. The self-cooling wafer polishing method according to claim 6, characterized in that: The material of the polishing pad is thermoplastic polyurethane.

8. The self-cooling wafer polishing method according to claim 1, characterized in that: The polishing rate of the polishing process is greater than 5 μm / h.

9. The self-cooling wafer polishing method according to claim 1, characterized in that: The surface roughness of the wafer obtained after the polishing process is less than 0.1 nm.

10. The self-cooling wafer polishing method according to claim 1, characterized in that: The step of performing a polishing process on the wafer further includes: The temperature between the polishing pad and the wafer is measured in real time by using a temperature measuring device.

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