A pre-polishing process for improving the scratch defect of silicon wafer polishing

Abstract

The application provides a pre-polishing process for improving the scratch defect of silicon wafer polishing, which is used in the field of semiconductor manufacturing technology and comprises the following steps: before the silicon wafer polishing process is performed, a double-sided polishing machine and a flexible polishing pad are used to trim the star wafer under a preset pressure. The flexible polishing pad is used for pre-trimming the new star wafer by exerting the preset pressure, so as to effectively remove the burrs, sharp corners and other micro protrusions on the surface and edge of the star wafer, improve the scratch defect caused by the falling of the burrs and other protrusions in the formal polishing process, and improve the polishing quality of the silicon wafer.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, and in particular relates to a pre-polishing process for improving scratch defects in silicon wafers. Background Technology

[0002] In semiconductor wafer manufacturing, the planetary polishing plate is a core fixture in the double-sided polishing process of large-size wafers. During polishing, the planetary polishing plate engages with the inner and outer gear rings of the equipment via its external teeth. The upper and lower polishing pads rotate in opposite directions, driving the planetary polishing plate to revolve and rotate, which in turn causes the silicon wafer to undergo planetary motion. This ensures uniform contact between the silicon wafer surface and the polishing pads, achieving polishing. The processing of the planetary polishing plate involves cutting and shaping processes, which can result in microscopic protrusions such as burrs on the substrate and inner liner surfaces. These microscopic protrusions detach from the planetary polishing plate during polishing, causing scratches on the silicon wafer surface. These scratches not only affect the surface quality of the silicon wafer but can also negatively impact subsequent semiconductor device manufacturing processes. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a pre-polishing process to improve the scratch defects in silicon wafer polishing. This process can effectively remove microscopic protrusions such as burrs and sharp corners from the surface and edges of the wafer, thereby reducing the scratch defects caused by burrs and other protrusions falling off during the formal polishing process and improving the polishing quality of the silicon wafer.

[0004] The technical solution adopted in this invention is: a pre-polishing process to improve the scratch defects of silicon wafer polishing. Before the silicon wafer polishing process, the planetary wafer is trimmed under a preset pressure using a double-sided polishing machine and a flexible polishing pad.

[0005] Furthermore, the trimming of the planetary plate includes the following steps:

[0006] The planetary plate is loaded into the double-sided polishing machine, and the double-sided polishing machine is run to bring the processing pressure to the preset pressure.

[0007] Adjust the pressure distribution of the upper and lower plates in sequence, and modify the surface shape of the upper and lower polishing pads;

[0008] The planetary plate was then subjected to rough polishing and fine polishing in sequence;

[0009] The planetary plate was ultrasonically cleaned.

[0010] Furthermore, the pressurization time to reach the preset pressure is 3 min to 6 min, and a coarse polishing liquid is introduced, the flow rate of which is 5 ml / s to 8 ml / s.

[0011] Furthermore, the sequential adjustment of the pressure distribution of the upper and lower plates is carried out in at least two stages, with each stage having a pressure of 1000 DaN to 1500 DaN and a pressurization time of 3 min to 6 min, and the coarse polishing fluid is introduced, with a flow rate of 5 ml / s to 8 ml / s.

[0012] Furthermore, during the coarse polishing, the pressure is 1000 DaN to 1500 DaN; the pressurization time is 40 min to 60 min; and the coarse polishing liquid is introduced, with a flow rate of 5 ml / s to 8 ml / s.

[0013] Furthermore, during the fine polishing process, the processing pressure is 1000 DaN to 1500 DaN; the pressurization time is 3 min to 6 min; and a fine polishing liquid is introduced, with a flow rate of 4 ml / s to 6 ml / s.

[0014] Furthermore, the flexible polishing pad is made of non-woven fabric with a thickness of 1.3mm to 1.45mm.

[0015] Furthermore, the coarse polishing solution comprises 15% to 30% silica particles with a particle size of 40 nm to 80 nm and a pH value of 10 to 12 at 20°C.

[0016] Furthermore, the polishing solution comprises 7% to 14% silica with a particle size of 25 to 50 nm and a pH value of 10 to 12 at 20°C.

[0017] Furthermore, before trimming the planetary plate, the flexible polishing pad is cleaned, including the following steps:

[0018] The flexible polishing pad is cleaned and roughened using the double-sided polishing machine and brush wheel.

[0019] The flatness of the flexible polishing pad is adjusted using the double-sided polishing machine and the correction wheel.

[0020] The advantages and positive effects of this invention are:

[0021] (1) This invention utilizes the flexible bonding and micro-grinding performance of the flexible polishing pad to pre-treat the new planetary wafer by applying a preset pressure, thereby effectively removing micro-protrusions such as burrs and sharp corners on the surface and edges of the planetary wafer, improving the scratch defects on the silicon wafer surface caused by burrs and other protrusions falling off during the formal polishing process, and improving the polishing quality of the silicon wafer.

[0022] (2) By using the method proposed in this invention to trim the planetary wafer, the flatness, thickness and size of the planetary wafer can be avoided while removing burrs, ensuring that it can stably support the silicon wafer in the formal polishing process, which is beneficial to improving the uniformity and surface quality of silicon wafer polishing. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] The specification and claims of this application, as well as the terms "first," "second," etc., used above, are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or apparatus.

[0025] In this document, references to "embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with an embodiment or implementation may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] Before introducing the technical solution of this application, let's go over the technical issues in related technologies in detail.

[0027] Polishing is a crucial step in silicon wafer manufacturing, used to remove surface defects and damage formed during cutting or grinding, ensuring that key indicators such as surface flatness, roughness, parallelism, and warpage meet chip processing requirements. Current silicon wafer polishing primarily employs double-sided polishing machines, which include independently rotating upper and lower polishing discs, a sun gear, and an external gear ring. During polishing, polishing pads are attached to both the upper and lower polishing discs. The silicon wafer rests on a planetary gear, which is placed on the polishing pad of the lower polishing disc. The outer ring of the planetary gear has external teeth that mesh between the sun gear and the external gear ring, and its interior has a receiving groove for placing the silicon wafer. The counter-rotation of the upper and lower polishing discs drives the planetary gear to revolve and rotate, thus inducing planetary motion in the silicon wafer, ensuring uniform contact between the wafer surface and the polishing pads, achieving polishing.

[0028] The planetary wheel, also known as a planetary plate or polishing fixture, is typically made of blued steel or fiberglass board in silicon wafer processing, formed through processes such as stamping or laser cutting, cleaning, and grinding. These processes can result in tiny burrs on the substrate and inner liner surfaces of the planetary wheel. When polishing a new planetary wheel, these burrs detach and scratch the silicon wafer surface. Current technology uses pre-polishing with test wafers to reduce scratches caused by burrs; however, this method is ineffective at removing burrs from the surface of new planetary wheels, resulting in severe scratches during the final polishing process. This also wastes considerable time and resources on test wafers, increasing costs and impacting production efficiency.

[0029] In view of this, to solve the above problems, this invention proposes a pre-polishing process to improve scratch defects in silicon wafer polishing. Specifically, before the silicon wafer polishing process, a planetary wafer is trimmed under a preset pressure using a double-sided polishing machine and a flexible polishing pad. Through this technical solution, before the formal silicon wafer polishing process starts, driven by the double-sided polishing machine, the flexible polishing pad is used to pre-trimme the new planetary wafer by applying a preset pressure, thereby effectively removing burrs, sharp corners and other micro-protrusions on the surface and edges of the planetary wafer. This improves the quality of silicon wafer polishing by preventing burrs and other protrusions from falling off and causing scratches on the silicon wafer surface during the formal polishing process.

[0030] In this embodiment, the flexible polishing pad differs from the polyurethane polishing pads used in existing polishing processes. Compared to polyurethane pads, the flexible polishing pad possesses better elasticity and flexibility, allowing it to adhere more closely to the surface of the planetary plate under preset pressure, forming a large-area uniform contact. Furthermore, the polishing fluid abrasive particles carried by the flexible polishing pad preferentially act on burrs, sharp corners, and other protrusions on the planetary plate surface, achieving precise and gentle removal of these protrusions without altering the plate's flatness, thickness, or dimensions. Simultaneously, the preset pressure enhances the abrasive particles' cutting ability against the planetary plate burrs. Thus, driven by the double-sided polishing machine, the planetary plate revolves and rotates, ensuring repeated and uniform contact between its front and back surfaces and the upper and lower flexible polishing pads, resulting in a smoothed and blunted surface and edges, achieving uniform finishing.

[0031] In addition, it is understandable that removing burrs from the surface of the planetarium plate can improve its dimensional accuracy and stability, enabling it to operate more stably during the formal polishing process, which in turn helps to improve the uniformity and surface quality of silicon wafer polishing.

[0032] Preferably, the flexible polishing pad is made of non-woven fabric with a thickness of 1.3mm to 1.45mm. The non-woven fabric polishing pad has several advantages: firstly, the non-woven fabric itself has good bulk and elasticity, allowing it to more closely conform to the microscopic contours of the wafer surface and avoid over-trimming; secondly, the interwoven fiber structure of the non-woven fabric can evenly bear the abrasive grains in the polishing fluid, resulting in a more uniform abrasive grain distribution; and thirdly, the non-woven fabric polishing pad has good wear resistance and is less prone to fiber shedding and other impurities, meeting the cleanliness requirements of the process. In some specific embodiments, the flexible polishing pad can also be used in formal silicon wafer polishing processes.

[0033] Preferably, the aforementioned flexible polishing pad is an old polishing pad used in the formal silicon wafer polishing process. The old polishing pad has a certain amount of wear, and its flexibility is better than that of the new polishing pad, so it can better adapt to the micro-contour of the planetarium surface.

[0034] Furthermore, in the above embodiments, in order to enable the old polishing pad to better achieve the dressing effect on the planetary plate, this application also proposes a method for cleaning and dressing the flexible polishing pad before dressing the planetary plate, including the following steps:

[0035] S1. Clean the flexible polishing pad using a double-sided polishing machine and a brush wheel;

[0036] The flexible polishing pad in this embodiment is an old polishing pad used in the formal silicon wafer polishing process. The flexible polishing pad includes an upper polishing pad and a lower polishing pad, which are respectively attached to the upper polishing disk and the lower polishing disk.

[0037] Before using this flexible polishing pad to finish the wafer, it is necessary to clean the pores of the pad to remove blockages. These blockages are formed during the actual polishing process and include tiny debris from the removed portion of the silicon wafer, abrasive particles from the polishing slurry that have broken down, and external dust and other impurities that may have gotten mixed in. Because the flexible polishing pad is made of a non-woven fabric with a porous structure, these impurities are adsorbed into the pores during the polishing process, preventing them from affecting the polishing quality of the silicon wafer.

[0038] The flexible polishing pad used in this embodiment is a flexible polishing pad that has been used in the polishing process for a period of time and has reached the middle and late stage of its service life. If it is not cleaned, the pore blockage will affect the uniformity of the distribution of the polishing liquid it carries and affect its finishing effect on the planetary plate. Therefore, it is necessary to clean the pore blockage on the flexible polishing pad first.

[0039] The aforementioned brush wheel is compatible with a double-sided polishing machine. Multiple brush sections are densely and evenly distributed on both the front and back surfaces of the body. Its outer edge is provided with external teeth that can mesh with the sun gear and external gear ring of the double-sided polishing machine. The brush wheel is installed between the upper polishing pad and the lower polishing pad. When the double-sided polishing machine is running, the brush wheel can revolve and rotate under the drive of the sun gear and the external gear ring, so that the brush can evenly act on various parts of the upper and lower polishing pads, while removing the blockages in the pores of the upper and lower polishing pads.

[0040] Specifically, in this step, the number of brush wheels mounted on the double-sided polishing machine can be one or more, and the cleaning time can be set according to the degree of pore blockage, which is not limited here; under the action of the brush wheels, all the pores on the upper and lower polishing pads are opened.

[0041] Furthermore, after opening the pores on the upper and lower polishing pads, remove the brush wheel and start the high-pressure water gun brushing program of the double-sided polishing machine to thoroughly remove the blockages brushed out by the brush wheel from the surface of the flexible polishing pad, ensuring that the surface of the flexible polishing pad is clean.

[0042] S2. Use a double-sided polishing machine and a correction wheel to adjust the flatness of the flexible polishing pad;

[0043] After cleaning the blockages on the upper and lower polishing pads, install the correction wheel on the double-sided polishing machine, positioning it between the upper and lower polishing pads. Run the dressing program to correct the upper and lower polishing pads, restoring them to a uniform and flat surface. This technical solution reduces the impact of the flexible polishing pad on the flatness of the planetary plate during dressing.

[0044] Understandably, when trimming the planetary plate, it is placed between the upper and lower polishing pads, and its flatness is directly affected by the surface shape of the upper and lower polishing pads. The surface shape of the upper and lower polishing pads is formed by the pressure distribution of the upper and lower polishing discs, as well as their own uniformity and flatness. Therefore, in this step, the uniformity and flatness of the upper and lower polishing pads are trimmed by the correction wheel, providing a good foundation for the subsequent surface shape adjustment of the upper and lower polishing pads.

[0045] The above-mentioned correction wheel and dressing process can adopt any existing structure and method capable of dressing the flexible polishing pad, and there are no restrictions here. Since some of the debris worn off by the correction wheel will still remain on the flexible polishing pad during the dressing process, it is necessary to clean the flexible polishing pad again with a high-pressure water gun to ensure that the surface of the flexible polishing pad is clean.

[0046] Furthermore, in this embodiment, after cleaning and trimming, the surface cleanliness and flatness of the flexible polishing pad meet the requirements for correcting planetary gears, and it can be used to trim planetary plates. The trimming of planetary plates includes the following steps:

[0047] S1. Load the planetary plate into the double-sided polishing machine; run the double-sided polishing machine to bring the pressure to the preset pressure;

[0048] Specifically, the new planetary polishers are precisely loaded into the planetary wheel mounting position of the double-sided polishing machine. The number of planetary polishers loaded is the same as the number loaded in the formal polishing process. Ensure that the planetary polishers are accurately positioned, without offset or looseness. After loading, confirm that the upper and lower plates of the polishing machine and the flexible polishing pad are in normal condition, and that the polishing fluid delivery pipeline is unobstructed. Then, start the double-sided polishing machine and gradually adjust the processing pressure according to the preset program, so that the upper and lower plates rotate in opposite directions, and the pressure applied to the planetary polishers rises steadily to the preset pressure.

[0049] In this embodiment, the preset pressure range in this step is preferably 1000 DaN to 1500 DaN, the time to reach the preset pressure is preferably 3 min to 6 min, and a coarse polishing fluid is introduced during the pressurization process, with a flow rate of 5 ml / s to 8 ml / s.

[0050] Specifically, this technical solution can be understood as follows: the preset pressure can be any one of 1000 DaN, 1100 DaN, 1200 DaN, 1300 DaN, 1400 DaN, 1500 DaN, or any value within the range of any two. The setting of the preset pressure enables the planetary plate to be subjected to uniform pressure from the upper polishing pad and the lower polishing pad, so that the upper polishing pad and the lower polishing pad are tightly attached to the surface of the planetary plate, forming a large-area uniform contact state.

[0051] The flow rate of the coarse polishing fluid can be any value from 5ml / s, 6ml / s, 7ml / s, 8ml / s, or any value within a range of any two, so that the coarse polishing fluid can be evenly distributed on the upper and lower polishing pads and fully contact all parts of the planetarium plate during the rotation of the upper and lower disks.

[0052] In this embodiment, the coarse polishing solution includes 15% to 30% silica particles with a particle size of 40 nm to 80 nm and a pH value of 10 to 12 at 20°C.

[0053] S2. Adjust the pressure distribution of the upper and lower plates in sequence to modify the surface shape of the upper and lower polishing pads;

[0054] After reaching the preset pressure, the surfaces of the upper and lower polishing pads are trimmed to ensure they are parallel and have the required flatness. This process is divided into at least two stages. In this embodiment, this step is divided into two stages: the upper plate adjustment stage and the lower plate adjustment stage, specifically including:

[0055] S201, Upper plate adjustment phase;

[0056] The double-sided polishing machine in this embodiment is equipped with a multi-zone pressure adjustment system for adjusting the pressure values ​​of different zones on the upper and lower plates. The upper and lower plates are divided into several zones, and the pressure of each zone is controlled by a different pressure adjustment unit. By controlling the pressure values ​​of different zones, the surface shape of the upper and lower polishing pads can be controlled.

[0057] The upper plate can be divided into regions as needed. For example, in this embodiment, the upper plate includes a central region, an inner ring region, an outer ring region, and multiple fan-shaped regions surrounding the outer ring region. According to the target surface shape requirements of the upper polishing pad, the pressure values ​​of different regions can be adjusted accordingly. For example, when the center of the upper polishing pad is high and the edge is low, the pressure in the central region can be increased and the pressure in the fan-shaped regions can be appropriately reduced. When the center of the upper polishing pad is low and the edge is low and high, the pressure in the central region can be reduced and the pressure in the fan-shaped regions can be appropriately increased.

[0058] In this embodiment, the upper plate adjustment stage is a dynamic adjustment process. The preset pressure range of this stage is preferably 1000 DaN to 1500 DaN, and dynamic adjustment is made based on the preset pressure. The pressurization time is preferably 3 min to 6 min. A coarse polishing liquid is introduced, and the flow rate of the coarse polishing liquid is 5 ml / s to 8 ml / s.

[0059] In this embodiment, the preset pressure in this stage can be the same as or different from the preset pressure in step S1, and can be set as needed; the preset pressure can be any one of 1000 DaN, 1100 DaN, 1200 DaN, 1300 DaN, 1400 DaN, 1500 DaN, or any value within the range of any combination of both; the coarse polishing solution includes 15% to 30% silica particles with a particle size of 40nm to 80nm and a pH value of 10 to 12 at 20°C; the flow rate of the coarse polishing solution can be any one of 5ml / s, 6ml / s, 7ml / s, 8ml / s, or any value within the range of any combination of both; the pressurization time can be any one of 3min, 4min, 5min, 6min, or any value within the range of any combination of both.

[0060] The pressure adjustment unit described above can be pneumatically driven, hydraulically driven, or other drive structures. In this embodiment, the pressure adjustment unit for each region is hydraulically driven. By adjusting the pressure of the pressure adjustment unit, the pressure of different regions of the upper plate acting on different parts of the upper polishing pad is adjusted. Under the combined action of the lower plate and the lower polishing pad, the upper polishing pad is adjusted to achieve the target surface shape.

[0061] S202, Lower-level adjustment phase;

[0062] Similarly, the area division of the lower plate can also be set as needed. For example, in this embodiment, the upper plate includes a central area, an inner ring area, an outer ring area, and multiple fan-shaped areas surrounding the outer ring area. The pressure values ​​of different areas are adjusted accordingly based on the target surface shape requirements of the upper polishing pad. The area division of the lower plate can be the same as that of the upper plate or different from that of the upper plate.

[0063] In this embodiment, the lower plate adjustment stage is also a dynamic adjustment process. The preset pressure range of this stage is preferably 1000 DaN to 1500 DaN, and dynamic adjustment is made based on the preset pressure. The pressurization time is preferably 3 min to 6 min. A coarse polishing liquid is introduced, and the flow rate of the coarse polishing liquid is 5 ml / s to 8 ml / s.

[0064] In this embodiment, the preset pressure in this stage can be the same as or different from the preset pressure in step S201, and can be set as needed; the preset pressure can be any one of 1000 DaN, 1100 DaN, 1200 DaN, 1300 DaN, 1400 DaN, 1500 DaN, or any value within the range of any two; the coarse polishing solution includes 15% to 30% silica particles with a particle size of 40nm to 80nm and a pH value of 10 to 12 at 20°C; the flow rate of the coarse polishing solution can be any one of 5ml / s, 6ml / s, 7ml / s, 8ml / s, or any value within the range of any two.

[0065] In this embodiment, the pressure adjustment unit of the lower plate also adopts a hydraulic drive structure. Through the action of the pressure adjustment unit, the pressure of different areas of the lower plate acting on different parts of the lower polishing pad is adjusted. Under the joint action of the upper plate and the upper polishing pad, the lower polishing pad is adjusted to achieve the target surface shape.

[0066] S3. Perform coarse polishing and fine polishing on the planetary plate in sequence;

[0067] After the upper and lower polishing pads are adjusted to achieve the set surface shape, the planetarium plate is subjected to rough polishing and fine polishing; this process is divided into at least two stages; in this embodiment, the step includes a rough polishing stage and a fine polishing stage, specifically including:

[0068] S301, coarse polishing stage;

[0069] During rough polishing, the upper and lower plates apply a preset pressure to the front and back of the planetarium plate through a flexible polishing pad. The preset pressure in this stage can be the same as or different from that in step S1 and / or step S2. In this embodiment, the preset pressure range is preferably 1000 DaN to 1500 DaN. The pressurization time is 40 min to 60 min, and a rough polishing liquid is introduced with a flow rate of 5 ml / s to 8 ml / s.

[0070] The preset pressure can be any one of 1000 DaN, 1100 DaN, 1200 DaN, 1300 DaN, 1400 DaN, 1500 DaN, or any value within the range of any combination of both; the flow rate of the coarse polishing fluid can be any one of 5 ml / s, 6 ml / s, 7 ml / s, 8 ml / s, or any value within the range of any combination of both; the pressurization time can be any one of 40 min, 45 min, 50 min, 50 min, 60 min, or any value within the range of any combination of both.

[0071] In the above process, the planetary wheel revolves and rotates within the double-sided polishing machine, closely adhering to the flexible polishing pad under preset pressure to form a large-area uniform contact state. Based on this, the polishing fluid abrasive particles carried by the flexible polishing pad rub against various parts of the planetary plate, including its surface, edges, and receiving grooves. It is understood that the particle size and particle size distribution of the abrasive particles in the polishing fluid will affect the polishing effect on the planetary plate. For example, when the particle size and particle size distribution are small, the polishing rate is lower, but the polishing effect is more uniform; when they are larger, although the polishing removal rate is faster, the uniformity is poor, which will affect the flatness of the planetary plate. Therefore, this invention designs the coarse polishing fluid used in the coarse polishing stage to include 15%–30% silica particles with a particle size of 40nm–80nm and a pH value of 10–12 at 20°C. This achieves a balance between polishing efficiency and uniformity in the coarse polishing stage and avoids affecting the flatness of the planetary plate.

[0072] After the rough polishing process, large burrs and protrusions on the surface of the planetarium plate are quickly and effectively removed.

[0073] S302, Fine polishing stage;

[0074] After rough polishing, in order to further improve the pre-polishing effect of the planetary plate, a fine polishing solution is introduced to further polish the planetary plate. In this embodiment, the fine polishing solution includes 7% to 14% silica with a particle size of 25 to 50 nm and a pH value of 10 to 12 at 20°C. By using abrasive grains with small particle size and particle size distribution, the surface of the planetary plate is finely and uniformly polished to remove small burrs and protrusions on the surface of the planetary plate.

[0075] In the above process, the preset pressure can be the same as or different from that in step S301; in this embodiment, the preset pressure range is preferably 1000 DaN to 1500 DaN; the pressurization time is 3 min to 6 min, and the flow rate of the polishing liquid is 4 ml / s to 6 ml / s.

[0076] The preset pressure can be any one of 1000 DaN, 1100 DaN, 1200 DaN, 1300 DaN, 1400 DaN, 1500 DaN, or any value within a range of any combination of both; the flow rate of the polishing solution can be any one of 5 ml / s, 6 ml / s, 7 ml / s, 8 ml / s, or any value within a range of any combination of both; and the pressurization time can be any one of 3 min, 4 min, 5 min, 6 min, or any value within a range of any combination of both.

[0077] After the fine polishing stage is completed, the processing pressure is gradually reduced according to the preset program. This process can be carried out in multiple stages. Finally, the planetary blade is unloaded from the double-sided polishing machine.

[0078] S4. Perform ultrasonic cleaning on the planetarium plate.

[0079] Ultrasonic cleaning can be performed in a planetary wheel cleaning machine for 8 to 12 minutes. Through ultrasonic cleaning, impurities on the surface of the planetary wheel can be removed, thereby ensuring the cleanliness of the planetary wheel. After cleaning, the planetary wheel is placed in a special library for storage, ready for use in the silicon wafer polishing process.

[0080] This technical solution effectively removes burrs from the surface of the new planetary wafer by trimming it before using it in the formal polishing process. This prevents burrs from falling off and scratching the silicon wafer surface during the formal polishing process, thus improving the scratch defects of the planetary wafer in the polishing process. At the same time, the flatness, thickness, and size of the planetary wafer do not change during the trimming process, ensuring that it can stably support the silicon wafer in the formal polishing process, which is conducive to improving the uniformity and surface quality of silicon wafer polishing.

[0081] Based on the above steps, specific embodiments of the present invention will be described in detail below:

[0082] Example 1

[0083] A method for cleaning and conditioning a flexible polishing pad, which has been used in a formal polishing process on a double-sided polishing machine and is nearing the end of its service life, is made of non-woven fabric. The upper polishing pad has a thickness of 1.3 mm, a hardness of 100 Asker C, and a compression rate of 5%; the lower polishing pad has a thickness of 1.3 mm, a hardness of 100 Asker C, and a compression rate of 5%. The method involves cleaning and conditioning the flexible polishing pad directly using the double-sided polishing machine without unloading it, specifically including the following steps:

[0084] S1. Clean the flexible polishing pad using a double-sided polishing machine and a brush wheel;

[0085] Install the brush wheel on the double-sided polisher, positioning it between the upper and lower polishing pads. Set the brush wheel program parameters and then run the double-sided polisher.

[0086] During this process, the upper plate speed is set to 3 rpm and the lower plate speed is set to 7 rpm, with the upper and lower plates rotating in opposite directions; the processing pressure is 150 DaN, clean water is introduced with a flow rate of 9 L / min, and the cleaning time is 7 min.

[0087] Then, the brush wheel was removed, and the high-pressure water gun brushing program of the double-sided polisher was started, with the cleaning time set to 7 minutes.

[0088] After cleaning, observe the pore blockage of the upper and lower polishing pads to ensure that the flexible polishing pads meet the requirements for pre-polishing.

[0089] S2. Use a double-sided polishing machine and a correction wheel to adjust the flatness of the flexible polishing pad;

[0090] Install the dressing wheel on the double-sided polishing machine, positioning it between the upper and lower polishing pads, and run the dressing program to dress the upper and lower polishing pads.

[0091] During this process, the upper plate speed is set to 3 rpm and the lower plate speed is set to 7 rpm, with the upper and lower plates rotating in opposite directions; the processing pressure is 150 DaN; pure water is used as the medium, with a pure water flow rate of 9 L / min and a cleaning time of 19 min.

[0092] The correction wheel was then removed, and the high-pressure water gun cleaning program on the double-sided polishing machine was restarted for 7 minutes.

[0093] After cleaning, observe the upper and lower polishing pads.

[0094] After cleaning, the flatness of the upper and lower polishing pads is tested using a dedicated testing device to ensure that the flatness of the flexible polishing pads meets the requirements for pre-polishing.

[0095] Example 2

[0096] A method for trimming a planetary wafer, wherein the planetary wafer in this embodiment is a new planetary wafer adapted to the double-sided polishing machine in Example 1, and is trimmed before being used in the formal polishing process; the wafer aperture of the planetary wafer is 300±1mm and the thickness is 775±5μm, and five planetary wafers are loaded at a time using the double-sided polishing machine in Example 1 and the cleaned and trimmed flexible polishing pad; the method specifically includes the following steps:

[0097] S1. Load the planetary plate into the double-sided polishing machine; run the double-sided polishing machine to bring the pressure to the preset pressure;

[0098] Five new planetary blades were placed on the lower polishing pad. The rotation speed of the upper plate was set to 12 rpm and the rotation speed of the lower plate to 25 rpm, with the upper and lower plates rotating in opposite directions. The preset pressure was 1000 DaN, the pressurization time was 6 minutes, and the coarse polishing fluid used had a flow rate of 8 L / min.

[0099] S2. Adjust the pressure distribution of the upper and lower plates in sequence to modify the surface shape of the upper and lower polishing pads;

[0100] S201, Upper plate adjustment phase;

[0101] The upper plate was set to rotate at 12 rpm, and the lower plate at 25 rpm, with the upper and lower plates rotating in opposite directions. The preset pressure was 1000 DaN, the pressurization time was 6 min, and the coarse polishing solution used contained 30% silica particles with a particle size of 40 nm to 80 nm, a pH of 11 at 20°C, and a flow rate of 8 L / min.

[0102] The shape of the disc is detected by sensors embedded in the disc surface. There are three sensors in total, distributed on the inner, middle and outer sides respectively. The disc shape is controlled by detecting the distance between the upper and lower discs. In order to achieve a disc surface where the upper and lower discs are parallel, the difference between the upper and lower disc gaps is preset to 0 in this embodiment.

[0103] S202, Lower-level adjustment phase;

[0104] After the upper plate is adjusted, the lower plate is adjusted. The rotation speed of the upper plate is set to 12 rpm and the rotation speed of the lower plate is set to 25 rpm. The rotation directions of the upper and lower plates are opposite. The preset pressure is 1000 DaN and the pressurization time is 6 min. The coarse polishing liquid in step S201 is used with a flow rate of 8 L / min.

[0105] The detection and control methods for disc accuracy are the same as in step S201.

[0106] S3. Perform coarse polishing and fine polishing on the planetary plate in sequence;

[0107] After the upper and lower polishing pads are adjusted to achieve the set surface shape, the planetarium plate is subjected to rough polishing and fine polishing; in this embodiment, this step includes a rough polishing stage and a fine polishing stage, specifically including:

[0108] S301, coarse polishing stage;

[0109] The upper plate is set to rotate at 12 rpm, and the lower plate at 25 rpm, with the upper and lower plates rotating in opposite directions. The preset pressure is 1000 DaN, the polishing time is 60 min, and the coarse polishing solution from step S201 is used at a flow rate of 8 L / min.

[0110] S302, Fine polishing stage;

[0111] The upper plate is set to rotate at 5 rpm and the lower plate at 10 rpm, with the upper and lower plates rotating in opposite directions. The preset pressure is 1000 DaN, the polishing time is 6 min, and the polishing solution used includes 14% silica with a particle size of 25-50 nm, a pH of 10-12 at 20℃, and a flow rate of 4-6 L / min.

[0112] S4. Perform ultrasonic cleaning on the planetarium plate.

[0113] After coarse and fine polishing, the planetary plate is unloaded and sent to a planetary wheel cleaner for ultrasonic cleaning. The ultrasonic frequency is set to 40KHz and the cleaning time is set to 4 minutes. Through ultrasonic cleaning, impurities on the surface of the planetary plate are removed.

[0114] In this embodiment, 10 sets of a total of 50 planetary plates were repaired. The surface of the planetary plates before and after repair was observed using a microscope, and it was found that there were no obvious burrs on the surface of the planetary plates.

[0115] Example 3

[0116] The silicon wafers were polished using the modified planetary wafers from Example 2. The silicon wafers were from the same batch that had undergone the slicing process. The silicon wafers with abnormal data were measured and removed. The initial values ​​of various tests such as surface roughness, warpage, curvature, and total thickness deviation of the remaining silicon wafers from the same batch were approximately the same. The silicon wafers were polished using the double-sided polishing machine from Examples 1 and 2 and the polishing process in the prior art.

[0117] The diameter of the silicon wafer is 300.02±0.0005mm. The double-sided polishing machine loads 5 trimmed planetary wafers each time, and each planetary wafer carries 3 silicon wafers. 15 silicon wafers are processed each time. The silicon wafers polished each time are divided into a test group, and 10 groups with a total of 150 silicon wafers are polished.

[0118] The front and back sides of the silicon wafers in each experimental group were inspected using a defect detector to obtain the average length of the scratches on the silicon wafers of the 10 experimental groups. After statistical analysis, the average length of the scratches on the front side of the polished silicon wafer was 47 mm, and the average length of the scratches on the back side was 55 mm.

[0119] Comparative Example 1

[0120] New, untreated planetary wafers from the same batch as those in Example 3 were used, and 10 sets of 50 planetary wafers were pre-polished using the existing pre-polishing process on the double-sided polishing machine in Example 3.

[0121] Subsequently, the same batch of silicon wafers as those in Example 3 were polished on the double-sided polishing machine in Example 3. The initial values ​​of various tests, such as surface roughness, warpage, curvature, and total thickness deviation of the silicon wafers, were approximately the same as those in Example 3.

[0122] The double-sided polishing machine loads 5 planetary blades at a time, and each planetary blade carries 3 silicon wafers. It processes 15 silicon wafers at a time. The silicon wafers polished each time are divided into a control group, and 10 groups of a total of 150 silicon wafers are polished.

[0123] The front and back sides of the silicon wafers in each control group were inspected using a defect detector to obtain the average length of scratches on the silicon wafers of the 10 control groups. After statistical analysis, the average length of scratches on the front side of the polished silicon wafer was 160 mm, and the average length of scratches on the back side was 240 mm.

[0124] By comparing the average length of the silicon wafer scratches in Example 3 with the average length of the silicon wafer scratches in Comparative Example 1, it can be clearly seen that the pre-polishing process provided by the present invention can significantly improve the scratch defects of silicon wafers in the polishing process and improve the polishing quality of silicon wafers.

[0125] The advantages and positive effects of this invention are:

[0126] (1) This invention utilizes the flexible bonding and micro-grinding performance of the flexible polishing pad to pre-treat the new planetary wafer by applying a preset pressure, thereby effectively removing micro-protrusions such as burrs and sharp corners on the surface and edges of the planetary wafer, improving the scratch defects on the silicon wafer surface caused by burrs and other protrusions falling off during the formal polishing process, and improving the polishing quality of the silicon wafer.

[0127] (2) By using the method proposed in this invention to trim the planetary wafer, the flatness, thickness and size of the planetary wafer can be avoided while removing burrs, ensuring that it can stably support the silicon wafer in the formal polishing process, which is beneficial to improving the uniformity and surface quality of silicon wafer polishing.

[0128] The advantages and positive effects of this invention are:

[0129] (1) This invention utilizes the flexible bonding and micro-grinding performance of the flexible polishing pad to pre-treat the new planetary wafer by applying a preset pressure higher than that of the formal polishing process, thereby effectively removing micro-protrusions such as burrs and sharp corners on the surface and edges of the planetary wafer, improving the scratch defects on the silicon wafer surface caused by burrs and other protrusions falling off during the formal polishing process, and improving the polishing quality of the silicon wafer.

[0130] (2) By using the method proposed in this invention to trim the planetary wafer, the flatness, thickness and size of the planetary wafer can be avoided while removing burrs, ensuring that it can stably support the silicon wafer in the formal polishing process, which is beneficial to improving the uniformity and surface quality of silicon wafer polishing.

[0131] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A pre-polishing process for improving scratch defects in silicon wafers, characterized in that: Before the silicon wafer polishing process, the planetary wafer is trimmed under preset pressure using a double-sided polishing machine and a flexible polishing pad.

2. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: The process of trimming the planetary plate includes the following steps: The planetary plate is loaded into the double-sided polishing machine, and the double-sided polishing machine is run to bring the processing pressure to the preset pressure. Adjust the pressure distribution of the upper and lower plates in sequence, and modify the surface shape of the upper and lower polishing pads; The planetary plate was then subjected to rough polishing and fine polishing in sequence; The planetary plate was ultrasonically cleaned.

3. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: The pressurization time to reach the preset pressure is 3 min to 6 min, and a coarse polishing fluid is introduced, with a flow rate of 5 ml / s to 8 ml / s.

4. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: The sequential adjustment of the pressure distribution of the upper and lower plates is carried out in at least two stages, with a pressure of 1000 DaN to 1500 DaN in each stage and a pressurization time of 3 min to 6 min. The coarse polishing fluid is introduced during this process, with a flow rate of 5 ml / s to 8 ml / s.

5. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: During the coarse polishing, the pressure is 1000 DaN to 1500 DaN; the pressurization time is 40 min to 60 min; and the coarse polishing liquid is introduced, with a flow rate of 5 ml / s to 8 ml / s.

6. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: During the fine polishing process, the processing pressure is 1000 DaN to 1500 DaN; the pressurization time is 3 min to 6 min; and a fine polishing liquid is introduced, with a flow rate of 4 ml / s to 6 ml / s.

7. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: The flexible polishing pad is made of non-woven fabric with a thickness of 1.3mm to 1.45mm.

8. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: The coarse polishing solution contains 15% to 30% silica particles with a particle size of 40 nm to 80 nm and a pH value of 10 to 12 at 20°C.

9. The pre-polishing process for improving scratch defects in silicon wafers according to claim 1, characterized in that: The polishing solution contains 7% to 14% silica with a particle size of 25 to 50 nm and a pH value of 10 to 12 at 20°C.

10. The pre-polishing process for improving scratch defects in silicon wafers according to any one of claims 1-8, characterized in that: Before trimming the planetary plate, the flexible polishing pad is cleaned, including the following steps: The flexible polishing pad is cleaned and roughened using the double-sided polishing machine and brush wheel. The flatness of the flexible polishing pad is adjusted using the double-sided polishing machine and the correction wheel.