Substrate polishing method and polishing table

Abstract

The invention provides a substrate grinding method and a grinding machine table. The method comprises the following steps: providing a substrate; placing the substrate on a carrying table, wherein the surface of the carrying table is a flat surface; introducing liquid between the surface of the carrying table and the back surface of the substrate to suspend the substrate; cooling to form a freezing layer between the surface of the carrying table and the back surface of the substrate; grinding the front surface of the substrate; raising the temperature to melt the freezing layer; and grinding the back surface of the substrate. According to the technical scheme, the grinding process for counteracting the fluctuation of the back face of the substrate based on the freezing layer effectively solves the problems existing in a traditional substrate grinding process, and the process yield can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials, and particularly to a substrate grinding method and a grinding machine. Background Art

[0002] In the process of semiconductor manufacturing, the grinding of the substrate is a crucial process, and its surface flatness directly affects the performance and manufacturing yield of subsequent devices. However, the back surface of the substrate is often not flat, with certain wavy undulations. Because the main ripples of the wafer (front and back) originate from the multi-wire sawing (MWS) process. In this process, the cutting wire swings slightly, and the thermal expansion of the machine will cause the wafer to generate a wavy profile. Such ripples are not rotationally symmetric but are distributed along the cutting direction. The amplitude of such ripples is in the range of several micrometers. Although it is difficult to completely eliminate such ripples in subsequent processes, the main steps to correct the wafer shape macroscopically are mechanical wafer processing processes such as grinding and grinding.

[0003] If such a substrate is directly ground, it will cause uneven stress on the substrate, which will in turn have a negative impact on the flatness of the front surface.

[0004] To solve this problem, the prior art usually fills the gap between the back surface of the substrate and the carrier with resin. The resin used first has a low viscosity, so that the wafer can float on the resin in a relaxed state, and the undulation of the back surface shape is compensated by the change in the resin layer thickness. After the wafer floats on the low-viscosity resin, the resin is hardened by ultraviolet curing to fix the wafer for the subsequent grinding process. However, this method has obvious defects. It is very difficult to completely remove the resin in subsequent processes. The residual resin will contaminate the substrate, affect the performance of the substrate and the progress of subsequent processes, and reduce the reliability and manufacturing efficiency of semiconductor devices.

[0005] Therefore, a new process method is needed to solve the problem of the back surface undulation of the substrate and avoid the adverse effects brought by resin residues. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a substrate grinding method and a grinding machine that can solve the problem of the back surface undulation of the substrate while avoiding the adverse effects brought by resin residues.

[0007] To solve the above problems, the present invention provides a substrate grinding method, including: providing a substrate; placing the substrate on a carrier, the surface of the carrier being a flat surface; introducing a liquid between the surface of the carrier and the back surface of the substrate to suspend the substrate; cooling to form a frozen layer between the surface of the carrier and the back surface of the substrate; grinding the front surface of the substrate; heating to melt the frozen layer; and grinding the back surface of the substrate.

[0008] Optionally, the liquid is water, and the formed frozen layer is an ice layer.

[0009] Optionally, the substrate is a single crystal silicon substrate.

[0010] Optionally, the stage has sidewalls that restrict the flow of liquid.

[0011] To solve the above problems, the present invention provides a grinding machine table, comprising: a stage for placing a substrate to be ground; a liquid adding device facing the gap between the stage and the substrate for introducing liquid between the surface of the stage and the back surface of the substrate; and a cooling device disposed below the stage for cooling the liquid and maintaining the temperature environment during the grinding process.

[0012] Optionally, the liquid is water, and the formed frozen layer is an ice layer.

[0013] Optionally, the substrate is a single crystal silicon substrate.

[0014] Optionally, the stage has sidewalls that restrict the flow of liquid.

[0015] Optionally, the liquid adding device includes a plurality of liquid adding holes disposed in the area on the surface of the stage where the substrate is placed for introducing liquid between the surface of the stage and the back surface of the substrate.

[0016] The grinding process based on the frozen layer to offset the undulation of the back surface of the substrate in the above technical solution effectively solves the problems existing in the traditional substrate grinding process and can improve the process yield. Description of the Drawings

[0017] Attached Figure 1 Shown is a schematic diagram of the implementation steps of the method according to a specific embodiment of the present invention.

[0018] Attached Figure 2A To attached Figure 2G Shown is a process flow diagram of the method according to a specific embodiment of the present invention. Detailed Description of the Embodiment

[0019] The following describes in detail the specific embodiments of the substrate grinding method and the grinding machine table provided by the present invention with reference to the drawings.

[0020] Attached Figure 1 Shown is a schematic diagram of the implementation steps of the method according to a specific embodiment of the present invention, including: step S10, providing a substrate; step S11, placing the substrate on a stage, the surface of the stage being a flat surface; step S12, introducing liquid between the surface of the stage and the back surface of the substrate to suspend the substrate; step S13, cooling to form a frozen layer between the surface of the stage and the back surface of the substrate; step S14, grinding the front surface of the substrate; step S15, heating up to melt the frozen layer; step S16, grinding the back surface of the substrate.

[0021] Appended Figure 2A To the appended Figure 2G The following shows the process flow chart of the method according to a specific embodiment of the present invention.

[0022] Appended Figure 2A As shown, referring to step S10: Provide a substrate 10. This specific embodiment particularly targets the case where both the front and back surfaces of the substrate 10 need to be ground and corrected for flatness. Therefore, the specific embodiment is illustrated with both the front and back surfaces having slight undulations. The substrate 10 can be selected from various types of semiconductor materials, such as single-crystalline silicon substrates, polycrystalline silicon substrates, compound semiconductor substrates (such as gallium arsenide, gallium nitride, etc.). In this specific embodiment, the substrate 10 is a single-crystalline silicon substrate. Single-crystalline silicon substrates have excellent electrical properties and crystal structure integrity and are widely used in the field of integrated circuit manufacturing. Their purity requirements are extremely high, and usually, the impurity content needs to be controlled at a very low level to ensure good electrical characteristics.

[0023] The size specifications of the substrate 10 need to be selected according to specific process requirements and equipment compatibility. Common substrate diameters include 4 inches, 6 inches, 8 inches, 12 inches, etc. With the continuous development of semiconductor technology, the application of larger-sized substrates is becoming more and more widespread. At the same time, the thickness of the substrate 10 also needs to be designed according to the actual situation, generally ranging from a few hundred micrometers to the millimeter level.

[0024] Appended Figure 2B As shown, referring to step S11: Place the substrate 10 on a stage 11, and the surface of the stage 11 is a flat surface. The stage 11 is a key component for carrying the substrate 10 and providing stable support for it. The surface flatness of the stage 11 is crucial for the fixation of the substrate 10 and the effect of subsequent grinding processes. To facilitate the subsequent introduction of liquid more easily, the stage 11 in this specific embodiment further includes a plurality of liquid addition holes 14 provided in the area on the surface of the stage 11 where the substrate 10 is placed.

[0025] The surface of the stage 11 needs to be processed. In this specific embodiment, since the subsequent technical solution of introducing liquid between the surface of the stage 11 and the back surface of the substrate 10 to suspend the substrate is adopted, the fluidity of the liquid can automatically fill the gap between the two and be evenly distributed. Therefore, the surface of the stage 11 does not require the extremely high flatness requirements in traditional processes. Specifically: The flatness tolerance of the surface of the stage 11 can be relaxed to the micrometer level (such as waviness ≤ 5μm), and only conventional machining (such as precision milling, grinding) is required to meet the usage requirements, without relying on nanoscale ultra-precision machining. Before cooling and solidifying, the liquid can adaptively fit the undulations of the back surface of the substrate through its own gravity and surface tension, while offsetting the local unevenness of the stage surface, so that the substrate can still maintain uniform overall stress after being fixed in the freezing layer, avoiding local stress concentration of the substrate caused by defects on the stage surface.

[0026] For the material selection of the carrier 11, more attention is paid to the heat conduction efficiency and chemical compatibility. Preferably, materials such as metals or graphite are required to have heat conductivity, chemical stability, and certain mechanical strength.

[0027] The material selection of the carrier 11 is also very crucial. Generally speaking, the carrier 11 needs to be made of materials with good thermal stability and mechanical strength, usually metals or graphite, etc. The selected materials should have a low coefficient of thermal expansion, high hardness, and good chemical stability, and can maintain dimensional stability at different process temperatures and environments, reducing the deformation of the carrier caused by temperature changes, so as to ensure the fixing accuracy of the substrate.

[0028] In summary, through the liquid suspension compensation mechanism, this solution significantly reduces the dependence on the flatness of the carrier surface, simplifies the carrier processing technology, and at the same time ensures the formation efficiency of the freezing layer and the substrate fixing accuracy through material optimization, taking into account both process reliability and cost advantages.

[0029] Appendix Figure 2C As shown, referring to step S12: Liquid is introduced between the surface of the carrier 11 and the back surface of the substrate 10 to suspend the substrate 10. The carrier 11 preferably has side walls that restrict the flow of the liquid to restrict the outward flow of the liquid.

[0030] This step is the preparation for the formation of the freezing layer and the cancellation of the undulation on the back surface of the substrate. The selected liquid needs to have a series of specific properties. First of all, the liquid should have good fluidity, be able to be evenly distributed between the surface of the carrier 11 and the back surface of the substrate 10, fill the tiny gaps, and ensure that the substrate can be evenly suspended. Secondly, the liquid should have a low freezing point and high purity to avoid impurity crystallization or other abnormal phenomena during the subsequent cooling process, which may affect the quality of the freezing layer. Common liquids can choose deionized water, ethylene glycol aqueous solution and other water-soluble organic solvents.

[0031] Deionized water has the advantages of high purity and stable chemical properties, and is a commonly used choice. Water-soluble organic solvents such as ethylene glycol water can reduce the freezing point by adding organic solvents, can remain liquid at lower temperatures, and are suitable for some process scenarios with lower cooling temperature requirements. When selecting a liquid, its compatibility with the materials of the carrier 11 and the substrate 10 also needs to be considered to avoid chemical reactions or corrosion phenomena.

[0032] The process of introducing the liquid needs to be precisely controlled. A special liquid delivery system can be used. In this specific embodiment, as shown in the appendix Figure 2CAs shown, a plurality of liquid injection holes 14 are provided on the surface of the stage 11 within the area for placing the substrate 10, which are used to introduce liquid between the surface of the stage 11 and the back surface of the substrate 10. The liquid is introduced into the gap between the surface of the stage 11 and the back surface of the substrate 10 at a certain flow rate and pressure. The control of the flow rate and pressure should be adjusted according to the size of the substrate 10, the structure of the stage 11, and the characteristics of the liquid to ensure that the liquid can uniformly fill the entire gap. Since the surface of the substrate 10 is hydrophobic, the substrate 10 can be stably suspended on the stage without flowing to the front surface through control. During the process of introducing the liquid, the flow rate, pressure, and liquid level of the liquid can be monitored in real time through sensors to ensure the stability and accuracy of the introduction process.

[0033] As attached Figure 2D As shown, refer to step S13: Cooling is performed to form a freezing layer 12 between the surface of the stage 11 and the back surface of the substrate 10. After the substrate 10 is suspended in the liquid, it needs to be cooled to solidify the liquid to form the freezing layer 12. The cooling process requires an efficient and precise cooling device 15, which is arranged below the stage 11 and is used to cool the liquid and maintain the temperature environment during the grinding process, such as a liquid nitrogen cooling system, a semiconductor refrigeration system, etc.

[0034] The cooling rate and the final temperature need to be strictly controlled according to the characteristics of the liquid and the process requirements. An overly fast cooling rate may cause stress and cracks inside the freezing layer 12, affecting its fixing effect and the subsequent removal process; while too low or too high a cooling temperature may affect the quality and performance of the freezing layer 12. Generally speaking, the cooling rate can be controlled, for example, between a few degrees Celsius to more than ten degrees Celsius per minute, and the final cooling temperature needs to be adjusted according to the freezing point of the selected liquid to ensure that the liquid can completely solidify to form a uniform and dense freezing layer.

[0035] During the cooling process, the temperature and state of the liquid need to be monitored in real time. By means of temperature sensors and imaging devices, etc., it is ensured that the liquid gradually solidifies to form a uniform and dense freezing layer 12. The freezing layer 12 should have sufficient strength and stability to firmly fix the substrate 10, and at the same time can melt smoothly without residue during the subsequent heating process.

[0036] As attached Figure 2EAs shown, refer to step S14: Grind the front side of the substrate 10. After the substrate 10 is firmly fixed on the stage 11 through the freezing layer 12, the front side of the substrate 10 is ground. The grinding process is mainly used to improve the flatness of the wafer surface, remove dicing damage, and adjust the thickness. Through the mechanical action of the rotating grinding disc and the grinding fluid, surface defects and undulations are removed layer by layer. Compared with the polishing process, the material removal amount of grinding is larger, and it is the core means in the rough machining stage. This process can also provide a basis for subsequent precision processes such as chemical mechanical polishing and lithography, directly affecting the yield and performance of semiconductor devices, and can achieve high-precision surface planarization. In this step, since the back side has been filled, the undulations on the back side are offset, so the grinding of the front side directly inherits the flatness of the stage 10. And the stage 10 can ensure extremely high flatness through mechanical processing, so the flatness of the front side in this step can meet the process requirements.

[0037] Attached Figure 2F As shown, refer to step S15: Raise the temperature to melt the freezing layer 12. After the front side of the substrate 10 is ground, it is necessary to melt the freezing layer 12 in order to perform subsequent operations on the substrate 10. Compared with the method using resin, this step is to remove pure water or a liquid doped with an organic solvent, so it can be operated at room temperature and there is no residue.

[0038] Specifically, the temperature increase process needs to be carried out slowly and evenly to avoid damaging the substrate 10 due to too rapid temperature changes. Multiple methods can be used to achieve temperature increase, such as heat conduction heating, radiation heating, etc. Heat conduction heating is achieved by contacting the stage 11 with a heating device and using the principle of heat conduction to transfer heat to the stage 11 and the freezing layer 12, so that its temperature gradually rises. Radiation heating uses radiation sources such as infrared rays and lasers to directly heat the freezing layer 12. The heating rate needs to be precisely controlled according to the thickness and material of the freezing layer 12 and the characteristics of the substrate 10. Generally speaking, the heating rate can be controlled, for example, between a few degrees Celsius and more than ten degrees Celsius per minute. Too fast a heating rate may cause large thermal stress inside the freezing layer 12, thus impacting the substrate 10 and even causing defects such as cracks. During the temperature increase process, the melting state of the freezing layer 12 needs to be monitored in real time. By means of temperature sensors, optical imaging devices, etc., the morphological changes and temperature distribution of the freezing layer 12 can be observed. When the freezing layer 12 is completely melted, the melted liquid needs to be drained in time to avoid liquid residue contaminating the substrate 10.

[0039] Attached Figure 2GAs shown, refer to step S16: Grind the back surface of the substrate 10. After the freezing layer 12 melts and discharges the liquid, turn the substrate 10 over so that its back surface faces up, and then perform grinding treatment on the back surface of the substrate 10. However, since the initial state of the back surface may be different from that of the front surface, appropriate adjustments need to be made in terms of process parameters and material selection. Before performing back grinding, it is necessary to clean and inspect the back surface of the substrate 10 to remove possible impurities and stains on the surface, and evaluate the initial flatness and defect conditions of the back surface. During the grinding process, it is also necessary to precisely control process parameters such as grinding pressure, grinding head rotation speed, and grinding fluid flow rate. Since the flatness of the back surface has been ensured to meet the process requirements during the previous process, this step can directly grind, that is, a flat substrate 10 that meets the process requirements is obtained.

[0040] Similar to front grinding, during back grinding, it is also necessary to monitor the grinding parameters and the quality of the back surface of the substrate in real time. By real-time feedback and adjustment of process parameters, ensure that the grinding effect of the back surface has good consistency with the front surface, thereby improving the flatness and surface quality of the entire substrate.

[0041] The grinding machine used in the above method includes: a stage for placing the substrate to be ground; a liquid adding device facing the gap between the stage and the substrate, used to introduce liquid between the surface of the stage and the back surface of the substrate; a cooling device arranged below the stage, used to cool the liquid and maintain the temperature environment during the grinding process.

[0042] The above technical solution effectively cancels out the undulations on the back surface of the substrate. Although resin filling can cancel out the undulations, there are residual problems. The above technical solution forms a freezing layer between the stage and the back surface of the substrate. Utilizing the fluidity of the liquid, first suspend and evenly distribute the substrate, and then cool to form a freezing layer. The freezing layer can closely fit the undulations on the back surface of the substrate and effectively cancel them out, enabling the substrate to be evenly stressed when grinding the front surface, thereby ensuring that the flatness of the front surface is not affected by the undulations on the back surface. Through actual testing, for the substrate processed by the process of the present invention, the flatness of the front surface has been significantly improved compared to the traditional direct grinding process, and indicators such as surface roughness are more in line with the requirements of high-precision semiconductor manufacturing.

[0043] It is very difficult to completely remove the resin residue in the subsequent process of the resin filling process, which will contaminate the substrate. However, the freezing layer used in the present invention can be completely removed after melting and will not leave any residual substances on the surface of the substrate. The melted liquid can be discharged through a simple drainage operation, avoiding contamination of the substrate, improving the cleanliness of the substrate, facilitating the smooth progress of the subsequent process, reducing the device defect rate caused by contamination, and improving the manufacturing yield of semiconductor devices.

[0044] In the process of the above technical solution, the formation and melting processes of the freezing layer can be achieved by precisely controlling the temperature and liquid parameters, with good repeatability and stability. In the processes of liquid introduction, cooling, and heating, etc., the parameters can be monitored and adjusted in real time through sensors to ensure the accuracy and consistency of the process. At the same time, during the grinding process, by monitoring and adjusting the process parameters in real time, the stability of the grinding quality can be guaranteed. This makes the entire process more stable and reliable, reduces the product quality differences caused by process fluctuations, and improves the production efficiency and product stability.

[0045] The resin filling process requires additional resin materials and complex removal processes, increasing the production cost and process time. However, the liquids used in the present invention (such as deionized water, ethylene glycol aqueous solution, etc.) have low costs, and the formation and removal processes of the freezing layer are relatively simple, without the need for complex equipment and processes. This not only reduces the production cost, but also shortens the process cycle, improves the production efficiency, and makes the semiconductor manufacturing process more economical and efficient.

[0046] In summary, the grinding process based on the freezing layer offsetting the substrate back surface undulation of the above technical solution effectively solves the problems existing in the traditional substrate grinding process through innovative process design and precise process control, has significant technical advantages and application values, and can bring important technical progress and economic benefits to the semiconductor manufacturing industry.

[0047] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A substrate grinding method, characterized in that, Comprising: Providing a substrate; Placing the substrate on a stage, the surface of the stage being a flat surface; Passing a liquid between the surface of the stage and the back surface of the substrate to suspend the substrate; Cooling to form a frozen layer between the surface of the stage and the back surface of the substrate; Grinding the front surface of the substrate; Heating up to melt the frozen layer; Grinding the back surface of the substrate.

2. The method according to claim 1, characterized in that The liquid is water, and the formed frozen layer is an ice layer.

3. The method according to claim 1, wherein The substrate is a single-crystalline silicon substrate.

4. The method according to claim 1, wherein The stage has side walls for restricting the flow of the liquid.

5. A grinding machine, characterized in that, Comprising: A stage for placing the substrate to be ground; A liquid adding device facing the gap between the stage and the substrate for passing a liquid between the surface of the stage and the back surface of the substrate; A cooling device arranged below the stage for cooling the liquid and maintaining the temperature environment during grinding.

6. The grinding machine table according to claim 5, characterized in that, The liquid is water, and the formed frozen layer is an ice layer.

7. The grinding machine according to claim 5, characterized in that The substrate is a single-crystalline silicon substrate.

8. The grinding machine according to claim 5, characterized in that, The stage has side walls for restricting the flow of the liquid.

9. The grinding machine table according to claim 5, wherein, The liquid adding device includes a plurality of liquid adding holes arranged in the area on the surface of the stage where the substrate is placed for passing a liquid between the surface of the stage and the back surface of the substrate.

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