A Control Method for the Flatness of Double-Sided Polishing of 12-Inch Recycled Wafers

Abstract

The present invention discloses a method for controlling the flatness of both sides of a 12-inch recycled wafer. The purpose of the present invention is to control the flatness of the 12-inch recycled wafer through a double-sided grinding device to achieve the target of TTV < 0.5um.

Description

Technical Field

[0001] The invention relates to a method for controlling the flatness of double-sided polishing of a 12-inch regenerated wafer. Background Art

[0002] The demand for test pieces in semiconductors continues to increase. To save costs, test piece regeneration projects have emerged. After the test pieces are used, their geometric parameters will be damaged to a certain extent, and their surface conditions will have pits and scratches. The regeneration project is to repair these test pieces so that they can be restored to the state when they were first tested and reused.

[0003] An important evaluation index in silicon wafer geometric parameters is the total thickness deviation (TTV). The evaluation of polished geometric parameters depends on whether the thickness uniformity of the silicon wafer surface is consistent after polishing. Customers also have high requirements for the surface flatness of silicon wafers. Therefore, when solving defects on the silicon wafer surface and improving intrinsic parameters, it is particularly important to accurately control the grinding thickness so that the thickness difference at various places on the silicon wafer surface is consistent.

[0004] There are two types of polishing methods in existing polishing technology: single-sided and double-sided.

[0005] Single-sided polishing relies on the mechanical action of the workpiece, polishing liquid and polishing disc. During the polishing process, local high temperature and high pressure are generated, causing physical and chemical changes to occur directly on the workpiece, so that the reactants on the surface of the workpiece are continuously polished away, thereby smoothing the surface of the workpiece. However, due to the uneven force on the front and back sides, it is difficult to achieve a large amount of grinding while ensuring the restoration of flatness.

[0006] Double-sided polishing equipment controls the processing of both sides of the workpiece at the same time, and can effectively avoid deformation problems caused by stress difference and bonding error during the process. However, the thickness difference of the workpieces processed together in the same polishing process cannot be too large, otherwise it will cause the grinding disc to tilt during the processing, causing the risk of product scratches, deformation and equipment damage. Therefore, for the recycled wafer workpiece whose incoming flatness has been destroyed, the degree of deformation inside the grinding disc will be higher than that of other product silicon wafers, making it difficult to control the flatness of the workpiece during the polishing process.

[0007] Based on this, this project provides a method for double-sided polishing of 12-inch recycled wafers, which can achieve high polishing volume while controlling flatness. Summary of the invention

[0008] The object of the present invention is to provide a method for controlling the flatness of double-sided polishing of a 12-inch regenerated wafer to solve the problems raised in the above-mentioned background technology.

[0009] To achieve the above objectives, the present invention provides the following technical solutions:.

[0010] A method for controlling the flatness of both sides of a 12-inch recycled wafer, the steps are as follows:

[0011] S1. Due to the poor uniformity of the incoming material, a low-speed mode with a starting pressure of 100 kg at low pressure, a clockwise rotation speed of 10 revolutions per minute for the upper polishing plate, and a counterclockwise rotation speed of 10 revolutions per minute for the lower polishing plate is adopted. Pressurize and increase the speed continuously and slowly at a fixed slope. The upper and lower polishing plates act on the silicon workpiece at the same time. The upper polishing plate sprays a rough polishing liquid at 24 °C and 6 L / min as a physical and chemical polishing medium, and continuously takes away the processing heat to maintain the stability of the processing state. At this time, among the same batch of processed products, the silicon workpieces with higher thickness are subject to greater physical friction, faster temperature change, and more obvious deformation. The polishing rate is slightly higher than that of other silicon workpieces. According to the corrosion rate of the polishing liquid used, the pressure increase time lasts for 5 minutes until it reaches a pressure of 300 kg, 31 clockwise rotations of the upper polishing plate, and 28 counterclockwise rotations of the lower polishing plate, and then it maintains stability;

[0012] S2. At this time, the surface thickness difference of the silicon workpiece can be reduced by 50%, and the uniformity is improved. A pressure of 600 kg is instantaneously applied by rapid pressure increase while the rotation speed remains unchanged. Uniform polishing is carried out by increasing the pressure. Specifically, according to the real-time temperature change of the temperature sensor inside the processing plate, the horizontality of the upper and lower polishing plates is adjusted through the oil pressure deformation of the local areas of the upper and lower polishing plates, so that the horizontality of the upper and lower polishing plates themselves reaches consistency. While continuously cutting the surface of the silicon workpiece, the consistency of the same batch of workpieces is improved, and this lasts for 10 minutes;

[0013] S3. After the thickness consistency of the silicon workpiece is improved, the pressure is instantaneously released to 300 kg, the rotation speed remains unchanged, the polishing liquid is switched to deionized water, and while continuously diluting and flushing the rough polishing liquid, the processing equipment is cooled down, and this lasts for 20 seconds;

[0014] S4. The pressure remains unchanged, the rotation speed ratio remains unchanged, the clockwise rotation speed of the upper polishing plate is reduced to 15.5 revolutions, and the counterclockwise rotation speed of the lower polishing plate is reduced to 14 revolutions. It is switched to a fine polishing liquid for surface improvement of the upper polishing plate, and a surfactant is used to hydrophilize the surface of the wafer to control the roughness and nano quality.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] The purpose of the present invention is to control the flatness of a 12-inch recycled wafer through a double-sided polishing device to achieve the goal of TTV < 0.5 μm.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] In view of the poor state of the incoming material and low flatness level before the processing of recycled silicon wafers, a unique processing technology is adopted to reprocess the surface of the silicon wafers.

[0019] 2. The specific implementation is achieved through four grinding stages. Brief Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the grinding device of the present invention.

[0021] Figure 2 It is a correlation diagram of the change in thickness difference of the present invention.

[0022] In the figure: 1 upper grinding disc, 2 lower grinding disc, 3 silicon workpiece. Embodiment

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Please refer to Figure 1-2 , the present invention provides a technical solution: a control method for the flatness of double-sided polishing of 12-inch recycled wafers, and the steps are as follows.

[0025] S1. Due to the poor uniformity of the incoming materials, a low-speed mode with a starting pressure of 100 kg, a clockwise rotation speed of 10 revolutions per minute for the upper grinding disc 1, and a counterclockwise rotation speed of 10 revolutions per minute for the lower grinding disc 2 is adopted. Pressurization and speed increase are carried out continuously and slowly at a fixed slope. The upper and lower grinding discs act on the silicon workpiece 3 at the same time. The upper grinding disc 1 sprays a rough polishing grinding fluid at 24 °C and 6 L / min as a physical and chemical grinding medium, and continuously takes away the processing heat to maintain the stability of the processing state. At this time, among the same batch of processed products, the silicon workpiece 3 with a higher thickness is subject to greater physical friction, faster temperature change, and more obvious deformation. The grinding rate is slightly higher than that of other silicon workpieces 3. According to the corrosion rate of the used grinding fluid, the pressure increase time lasts for 5 minutes until it reaches a pressure of 300 kg, the upper grinding disc 1 rotates clockwise 31 times, and the lower grinding disc 2 rotates counterclockwise 28 times and then maintains stability.

[0026] S2. At this time, the surface thickness difference of the silicon workpiece 3 can be reduced by 50%, and the uniformity is improved. Instantaneous pressure increase is adopted to reach a pressure of 600 kg acting on both sides of the workpiece, and the rotation speed remains unchanged. Unified grinding is carried out by increasing the pressure. Emphasis is placed on adjusting the oil pressure deformation of the local areas of the upper and lower grinding discs according to the real-time temperature change of the temperature sensor inside the processing disc, so that the flatness of the upper and lower grinding discs themselves reaches consistency. While continuously cutting the surface of the silicon workpiece 3, the consistency of the same batch of workpieces is improved, and it lasts for 10 minutes.

[0027] S3. After the thickness consistency of the silicon workpiece 3 is improved, instantaneously relieve the pressure to 300 kg, keep the rotation speed unchanged, switch the grinding fluid to deionized water, continuously dilute and flush the rough polishing fluid while cooling the processing equipment for 20 seconds;

[0028] S4. Keep the pressure unchanged and maintain the rotation speed ratio unchanged. The clockwise rotation speed of the upper grinding plate 1 is reduced to 15.5 revolutions, and the counterclockwise rotation speed of the lower grinding plate 2 is reduced to 14 revolutions. Switch to the fine polishing fluid to improve the surface of the upper grinding plate 1, and use a surfactant to hydrophilize the wafer surface and control the roughness and nano-quality.

[0029] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the flatness of double-sided polishing of a 12-inch recycled wafer, characterized in that: The steps are as follows: S1. Due to the poor uniformity of the incoming materials, start with a low pressure of 100 kg. Adopt a low-speed mode where the upper grinding plate (1) rotates clockwise at 10 revolutions per minute and the lower grinding plate (2) rotates counterclockwise at 10 revolutions per minute. Continuously and slowly increase the pressure and rotational speed at a fixed slope. The upper and lower grinding plates act on the silicon workpiece (3) simultaneously. The upper grinding plate (1) sprays a rough polishing grinding fluid at 24 degrees Celsius and 6 L / min as the physical and chemical grinding medium, and continuously removes the processing heat to maintain the stability of the processing state. At this time, among the same batch of processed products, the silicon workpiece (3) with a higher thickness is subject to greater physical friction, has a faster temperature change, and more obvious deformation. The grinding rate is slightly higher than that of other silicon workpieces (3). According to the corrosion rate of the used grinding fluid, the pressure increase time lasts for 5 minutes until it reaches a pressure of 300 kg, the upper grinding plate (1) rotates 31 times clockwise, and the lower grinding plate (2) rotates 28 times counterclockwise and then maintains stability. S2. At this time, the surface thickness difference of the silicon workpiece (3) can be reduced by 50%, and the uniformity is improved. Adopt instant pressure increase to reach a pressure of 600 kg acting on both sides of the workpiece, and keep the rotational speed unchanged. Uniformly grind by increasing the pressure. Focus on the real-time temperature change of the internal temperature sensor of the processing plate, and adjust the oil pressure deformation of the local areas of the upper and lower grinding plates to make the levelness of the upper and lower grinding plates themselves consistent. While continuously cutting the surface of the silicon workpiece (3), improve the consistency of the same batch of workpieces, lasting for 10 minutes. S3. After the thickness consistency of the silicon workpiece (3) is improved, instantaneously release the pressure to 300 kg, keep the rotational speed unchanged, switch the grinding fluid to deionized water, continuously dilute and flush the rough polishing fluid while cooling the processing equipment, lasting for 20 seconds. S4. Keep the pressure unchanged and maintain the rotational speed ratio unchanged. The clockwise rotational speed of the upper grinding plate (1) is reduced to 15.5 revolutions, and the counterclockwise rotational speed of the lower grinding plate (2) is reduced to 14 revolutions. Switch to a fine polishing fluid to improve the surface of the upper grinding plate (1), use a surfactant treatment to hydrophilize the wafer surface, and control the roughness and nano-quality.

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