Processing methods for improving silicon wafer flatness

Abstract

This invention relates to a method for improving the flatness of silicon wafers. The method includes the following steps: providing a polished silicon wafer; immersing the silicon wafer in a mixed acid solution while simultaneously rotating the silicon wafer; the mixed acid solution comprising hydrofluoric acid, nitric acid, and an organic polychain alcohol, wherein the volume percentage of the organic polychain alcohol is 0.4% to 0.6%, and the rotational speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohol increases. This invention effectively improves the flatness of the polished silicon wafer, reduces or suppresses edge effects, and achieves effective control of the etching rate.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a processing method for improving the flatness of silicon wafers. Background Technology

[0002] In the manufacturing process of semiconductor integrated circuits, silicon wafers, as the core substrate material, directly affect the precision of subsequent key processes such as photolithography, etching, thin film deposition, and ion implantation, thereby determining the electrical performance, reliability, and yield of semiconductor devices. Silicon wafers undergo multiple precision processing steps during production, including crystal growth, slicing, grinding, etching, cleaning, and inspection. Among these, grinding is the core step for achieving uniform silicon wafer thickness. However, traditional grinding processes are affected by factors such as the flatness of the grinding pad surface, the uniformity of grinding pressure distribution, the particle size distribution of the grinding particles, and the stability of the grinding slurry supply. This results in silicon wafers with significant thickness deviations, surface roughness, pronounced edge effects, localized highs and lows, and residual microscopic damage after grinding, leading to a high total thickness variation (TTV) that cannot directly meet the requirements of high-end semiconductor devices.

[0003] To improve the flatness of polished silicon wafers, the current main method is chemical etching. However, traditional methods of improving the flatness of polished silicon wafers through chemical etching have the following problems: First, due to uneven contact between the silicon wafer surface and the etching solution, over-etching at the edges and insufficient etching at the center are prone to occur, resulting in limited flatness improvement and even exacerbating thickness deviations, leading to defects such as edge collapse and center bulges; Second, the etching rate is difficult to control precisely, which can easily lead to flatness deterioration due to excessively fast or slow etching rates; Third, the initial reaction is intense, resulting in a much deeper etching depth at the edges of the silicon wafer than at the center, creating a significant edge effect that is difficult to correct through subsequent processes.

[0004] Therefore, how to effectively improve the flatness of silicon wafers after grinding, reduce or suppress the occurrence of edge effects, and achieve effective control of the corrosion rate, so as to improve the flatness of silicon wafers after wet cleaning and thus meet the needs of high-end semiconductor devices, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This invention provides a processing method for improving the flatness of silicon wafers, which effectively improves the flatness of silicon wafers after grinding, reduces or suppresses the occurrence of edge effects, and achieves effective control of the etching rate, thereby improving the flatness of silicon wafers after wet cleaning and meeting the requirements of high-end semiconductor devices.

[0006] According to some embodiments, the present invention provides a method for improving the flatness of silicon wafers, comprising the following steps: Provide a polished silicon wafer; The silicon wafer is immersed in a mixed acid solution and simultaneously driven to rotate. The mixed acid solution includes hydrofluoric acid, nitric acid, and organic polychain alcohols. The organic polychain alcohols account for 0.4% to 0.6% of the volume percentage of the mixed acid solution, and the rotation speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohols in the mixed acid solution increases.

[0007] In some embodiments, before immersing the silicon wafer in the mixed acid solution, the following steps are further included: The silicon wafer is cleaned using an ultrasonic cleaning process to remove impurities, including particulate matter, adhering to the surface of the silicon wafer.

[0008] In some embodiments, after cleaning the silicon wafer using an ultrasonic cleaning process, the following steps are further included: The silicon wafer is subjected to alkaline etching treatment in an alkaline bath.

[0009] In some embodiments, the specific steps of immersing the silicon wafer in a mixed acid solution and simultaneously driving the silicon wafer to rotate include: An acid tank containing the mixed acid solution is provided, and a rotating shaft is provided in the middle of the acid tank; The silicon wafer is fixed on the rotating shaft, and the silicon wafer is completely immersed in the mixed acid solution, and the rotating shaft is driven to rotate.

[0010] In some embodiments, the volume ratio of the hydrofluoric acid, the nitric acid, and the organic polychain alcohol in the mixed acid solution is V. 氢氟酸 V 硝酸 V 有机多链醇类 =2:197: (0.8~1.2).

[0011] In some embodiments, the specific steps of fixing the silicon wafer to the rotating shaft, completely immersing the silicon wafer in the mixed acid solution, and driving the rotating shaft to rotate further include: The temperature of the mixed acid solution in the acid tank is controlled at 20℃±2℃, and the rotation speed of the shaft is controlled at 5rpm~10rpm.

[0012] In some embodiments, the specific steps of fixing the silicon wafer to the rotating shaft, completely immersing the silicon wafer in the mixed acid solution, and driving the rotating shaft to rotate further include: Determine whether the volume percentage of the organic polychain alcohol is greater than or equal to 0.4% and less than 0.5%. If so, control the rotation speed of the shaft to 8 rpm to 10 rpm. Determine whether the volume percentage of the organic polychain alcohol is greater than or equal to 0.5% and less than or equal to 0.6%. If so, control the rotation speed of the shaft to 5 rpm to 7 rpm.

[0013] In some embodiments, before immersing the silicon wafer in the mixed acid solution, the following steps are further included: The silicon wafer is pre-impregnated in a pre-impregnation solution containing organic polychain alcohols, wherein the concentration of the organic polychain alcohols in the pre-impregnation solution is 0.1 to 0.5 times the concentration of the organic polychain alcohols in the mixed acid solution.

[0014] In some embodiments, the specific steps of immersing the silicon wafer in a mixed acid solution and simultaneously driving the silicon wafer to rotate further include: Adjust the acid etching parameters to control the etching rate of the silicon wafer by the mixed acid solution to be 5.5 μm / min to 10 μm / min. The acid etching parameters include any one or a combination of two or more of the following: the temperature of the mixed acid solution, the rotation speed of the silicon wafer, and the composition of the mixed acid solution.

[0015] In some embodiments, after immersing the silicon wafer in a mixed acid solution and simultaneously driving the silicon wafer to rotate, the following steps are further included: The silicon wafer was placed in a mixed environment of hydrofluoric acid and ozone for cleaning and drying; The silicon wafer is placed in an ozone oxidation bath for oxidation treatment, and a protective oxide film is generated on the surface of the silicon wafer.

[0016] The present invention provides a method for improving the flatness of silicon wafers. The method involves immersing a polished silicon wafer in a mixed acid solution while simultaneously rotating the wafer. The mixed acid solution comprises hydrofluoric acid, nitric acid, and organic polychain alcohols. The organic polychain alcohols constitute 0.4% to 0.6% of the volume of the mixed acid solution, and the rotational speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohols in the mixed acid solution increases. On the one hand, the organic polychain alcohols serve as highly efficient wetting agents and corrosion inhibitors in the acid etching process, enabling the mixed acid solution to form a uniform thickness on the surface of the silicon wafer. A uniform liquid film layer is formed, and the volume percentage of the organic polychain alcohol in the mixed acid solution is controlled at 0.4%~0.6%, avoiding problems of excessive or insufficient corrosion in certain areas, thus improving the uniformity of acid etching of the silicon wafer. On the other hand, by synergistically controlling the volume percentage of the organic polychain alcohol and the rotation speed of the silicon wafer, the rotation speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohol increases. This enhances the fluidity and uniform coverage of the liquid film while avoiding liquid film fluctuations and splashing, ensuring the stability and controllability of the acid etching process, and achieving synchronous and uniform etching of the entire surface of the silicon wafer. The synergistic effect of the above two aspects effectively improves the flatness of the silicon wafer after polishing, reduces or suppresses the occurrence of edge effects, and achieves effective control of the etching rate. This results in improved flatness of the silicon wafer after wet cleaning; for example, the total thickness change of the silicon wafer after acid etching can be stably reduced to 0.28μm~0.35μm, thereby meeting the requirements of high-end semiconductor devices.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of a processing method for improving silicon wafer flatness in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a silicon wafer subjected to acid etching in a specific embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures 20 acid tanks 21 silicon wafer 22-spindle Detailed Implementation The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This specific embodiment provides a method for improving the flatness of silicon wafers. Figure 1 This is a flowchart of a processing method for improving silicon wafer flatness in a specific embodiment of the present invention. For example... Figure 1 As shown, the method for improving silicon wafer flatness includes the following steps: Step S11: Provide a polished silicon wafer; Step S12: Immerse the silicon wafer in a mixed acid solution and simultaneously drive the silicon wafer to rotate. The mixed acid solution includes hydrofluoric acid, nitric acid, and organic polychain alcohols. The organic polychain alcohols account for 0.4% to 0.6% of the volume percentage of the mixed acid solution, and the rotation speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohols in the mixed acid solution increases.

[0022] In some embodiments, before immersing the silicon wafer in the mixed acid solution, the following steps are further included: The silicon wafer is cleaned using an ultrasonic cleaning process to remove impurities, including particulate matter, adhering to the surface of the silicon wafer.

[0023] Specifically, the ultrasonic cleaning process is used to repeatedly clean the polished silicon wafer multiple times (e.g., three times) to thoroughly remove impurities, including polishing particles, metallic impurities, organic contaminants, polishing debris, and other particulate matter attached to the surface of the silicon wafer, so as to avoid the impurities causing defects such as localized corrosion abnormalities, pinholes, and pits during subsequent corrosion (e.g., acid corrosion).

[0024] In some embodiments, after cleaning the silicon wafer using an ultrasonic cleaning process, the following steps are further included: The silicon wafer is subjected to alkaline etching treatment in an alkaline bath.

[0025] Specifically, after cleaning the silicon wafer using the ultrasonic cleaning process, the silicon wafer is transferred to an alkaline bath containing an alkaline etching solution, ensuring the silicon wafer is completely immersed in the solution. This uniformly removes mechanical damage layers, microcracks, residual stress, and other defects on the silicon wafer surface caused by grinding, thus initially etching the surface of the silicon wafer, initially correcting thickness deviations, and subsequently reducing surface roughness. This achieves initial surface leveling of the silicon wafer and provides a uniform, stable, and undamaged base surface for subsequent acid etching. In one example, the alkaline etching solution includes potassium hydroxide.

[0026] Figure 2 This is a schematic diagram of the structure of a silicon wafer subjected to acid etching in a specific embodiment of the present invention. In some embodiments, the specific steps of immersing the silicon wafer in a mixed acid solution and simultaneously driving the silicon wafer to rotate include: An acid tank 20 is provided to contain the mixed acid solution, and the acid tank 20 has a rotating shaft 22 in the middle. The silicon wafer 21 is fixed on the rotating shaft 22, and the silicon wafer 21 is completely immersed in the mixed acid solution, and the rotating shaft 22 is driven to rotate.

[0027] Specifically, after the mixed acid solution is transferred to the acid tank 20, the silicon wafer 21, which has undergone the alkaline etching treatment, is fixed on the rotating shaft 22 in the middle of the acid tank 20, so that the silicon wafer 21 is completely immersed in the mixed acid solution. Then, the rotating shaft 22 is driven to rotate, and the rotation of the rotating shaft 22 causes the silicon wafer 21 located on it to rotate synchronously, ensuring that the mixed acid solution evenly covers the surface of the silicon wafer 21.

[0028] In some embodiments, the volume ratio of the hydrofluoric acid, the nitric acid, and the organic polychain alcohol in the mixed acid solution is V. 氢氟酸 V 硝酸 V 有机多链醇类 =2:197: (0.8~1.2).

[0029] Specifically, the mixed acid solution includes hydrofluoric acid, nitric acid, and organic polychain alcohols. The nitric acid acts as a strong oxidizing agent, oxidizing the Si on the surface of the silicon wafer 21 to SiO2. The hydrofluoric acid dissolves the SiO2. Thus, through the synergistic effect of the hydrofluoric acid and nitric acid, continuous and uniform etching of the silicon wafer 21 surface is achieved. In this specific embodiment, the organic polychain alcohols refer to long-chain fatty alcohols with 12 to 18 carbon atoms. As an example, the organic polychain alcohols can be selected from one or more of the following alcohols: cetyl alcohol, stearyl alcohol, oleyl alcohol (unsaturated octadecyl alcohol), myristyl alcohol, etc. The aforementioned alcohols all possess similar amphiphilic structures, enabling them to regulate surface tension and inhibit corrosion in the mixed acid solution. This allows the mixed acid solution to uniformly coat the entire surface of the silicon wafer 21, forming a liquid film layer of uniform thickness, high stability, and moderate fluidity. This prevents excessive or insufficient localized corrosion, ensuring uniform and gentle etching of the silicon wafer 21 and significantly improving its surface flatness. The volume ratio of the hydrofluoric acid, nitric acid, and organic polychain alcohols in the mixed acid solution is V... 氢氟酸 V 硝酸 V 有机多链醇类 =2:197:(0.8~1.2), thereby effectively controlling the rate of corrosion of the silicon wafer 21 by the mixed acid solution, effectively suppressing the edge over-corrosion and local roughness of the silicon wafer, and ensuring effective improvement of the flatness of the silicon wafer after corrosion. In the following embodiments, myristol is used as an example to illustrate the technical effect of this specific embodiment. However, those skilled in the art should understand that using other organic polychain alcohols with 12~8 carbon atoms (such as cetyl alcohol, stearyl alcohol, oleyl alcohol, etc.) to replace myristol can achieve basically the same technical effect under the same process conditions (the corrosion rate deviation of different types of organic polychain alcohols is within ±0.5μm / min, and the TTV deviation is within ±0.03μm). These alternative solutions all fall within the protection scope of this invention. Therefore, the data obtained in the following embodiments can be reasonably expected to be applicable to all organic polychain alcohols (i.e., cetyl alcohol, stearyl alcohol, oleyl alcohol, myristol, etc.) limited to this specific embodiment.

[0030] Table 1 shows the effect of mixed acid solutions with different concentrations of organic polychain alcohols on the flatness improvement of silicon wafers. The organic polychain alcohols used in all examples and comparative examples in Table 1 are the same type (i.e., myristol). As shown in Table 1, when the volume fraction of the organic polychain alcohol in the mixed acid solution is in the range of 0.8-1.2 (i.e., the volume percentage of the organic polychain alcohol in the mixed acid solution is 0.4%~0.6%) (i.e., Examples 1, 2, and 3), the acid etching rate is controlled between 5.5-10 μm / min, and the total thickness change (TTV) of the silicon wafer after acid etching is in the range of 0.28 μm~0.35 μm. Compared with the silicon wafer after alkaline etching (TTV approximately 0.55 μm), the flatness improvement rate reaches 38%-48%. Among them, Example 2 (volume fraction of organic polychain alcohol is 1.0) shows the best effect. Comparative Examples 1, 2, and 3 show the flatness improvement results when the volume fraction of organic polychain alcohols in the mixed acid solution exceeds 0.8-1.2 (i.e., the volume percentage of organic polychain alcohols in the mixed acid solution exceeds 0.4%-0.6%). As shown in Comparative Examples 1 and 2, when the volume fraction of organic polychain alcohols in the mixed acid solution is less than 0.8%, the acid etching rate is too fast (e.g., reaching 11.4 μm / min to 12.5 μm / min), resulting in over-etching or localized surface roughness at the edges of the silicon wafer after acid etching, with a flatness improvement rate of only 5%-13%. As shown in Comparative Example 3, when the volume fraction of organic polychain alcohols in the mixed acid solution is greater than 1.2%, the acid etching rate is too slow (e.g., only 3.8 μm / min), and the organic residue on the surface of the silicon wafer increases after acid etching, resulting in a negative flatness improvement rate (i.e., flatness degradation). Therefore, it can be seen that a good flatness improvement effect can only be obtained when the volume fraction of organic polychain alcohols in the mixed acid solution is in the range of 0.8-1.2 (that is, the volume percentage of organic polychain alcohols in the mixed acid solution is 0.4%~0.6%).

[0031] Table 1. Comparison of the effects of mixed acid solutions with different concentrations of organic polychain alcohols on silicon wafer flatness.

[0032] In some embodiments, the specific steps of fixing the silicon wafer 21 to the rotating shaft 22, making the silicon wafer 21 completely immersed in the mixed acid solution, and driving the rotating shaft 22 to rotate further include: The temperature of the mixed acid solution in the acid tank 20 is controlled at 20℃±2℃, and the rotation speed of the rotating shaft 22 is controlled at 5rpm~10rpm.

[0033] Specifically, during the acid etching process of the silicon wafer 21 in the acid tank 20, the temperature of the mixed acid solution in the acid tank 20 is controlled at 20℃±2℃, and the rotation speed of the rotating shaft 22 is controlled at 5rpm~10rpm to stabilize the acid etching rate, avoid excessive edge etching due to excessive temperature and residue accumulation due to excessive temperature, and ensure that the mixed acid solution forms a uniform and stable liquid film on the surface of the silicon wafer 21, avoiding uneven etching due to excessively low rotation speed and droplet splashing and liquid film rupture due to excessively high rotation speed.

[0034] In some embodiments, the specific steps of fixing the silicon wafer 21 to the rotating shaft 22, making the silicon wafer 21 completely immersed in the mixed acid solution, and driving the rotating shaft 22 to rotate further include: Determine whether the volume percentage of the organic polychain alcohol is greater than or equal to 0.4% and less than 0.5%. If so, control the rotation speed of the rotating shaft 22 to 8 rpm to 10 rpm. Determine whether the volume percentage of the organic polychain alcohol is greater than or equal to 0.5% and less than or equal to 0.6%. If so, control the rotation speed of the rotating shaft 22 to 5 rpm to 7 rpm.

[0035] Specifically, when the volume percentage of the organic polychain alcohol in the mixed acid solution is greater than or equal to 0.4% and less than 0.5%, the concentration of the organic polychain alcohol is relatively low, resulting in a relatively high surface tension of the mixed acid solution. Therefore, the rotation speed of the silicon wafer 21 needs to be increased, for example, by controlling the rotation speed of the shaft 22 to 8 rpm to 10 rpm, to enhance the fluidity and uniform coverage of the liquid film and prevent excessively rapid edge etching of the silicon wafer 21. When the volume percentage of the organic polychain alcohol in the mixed acid solution is greater than or equal to 0.5% and less than or equal to 0.6%, the concentration of the organic polychain alcohol is relatively high, resulting in a relatively strong wetting ability of the mixed acid solution. Therefore, the rotation speed of the silicon wafer 21 needs to be reduced, for example, by controlling the rotation speed of the shaft 22 to 5 rpm to 7 rpm, to avoid problems such as acid splashing, liquid film rupture, or insufficient etching at the center of the silicon wafer due to excessively high rotation speed, thereby further ensuring uniform overall etching and optimal flatness of the silicon wafer.

[0036] Table 2 shows the verification results of the linkage between different concentrations of organic polychain alcohols and different rotation speeds. The organic polychain alcohols used in all examples and comparative examples in Table 2 are the same type (i.e., all are myristol). As shown in Table 2, as in Example 4, a high rotation speed of 9 rpm was used when the volume percentage of the organic polychain alcohol was 0.45% (low concentration); as in Example 5, a low rotation speed of 6 rpm was used when the volume percentage of the organic polychain alcohol was 0.55% (high concentration). The results of Examples 4 and 5 show that the acid layer thickness deviation was controlled within ±0.25 μm, the TTV (total thickness change) after acid corrosion was 0.29-0.31 μm, and the edge corrosion uniformity was rated as excellent. Comparative Examples 4 and 5 used opposite rotation speed matching relationships; that is, the low concentration of Comparative Example 4 was matched with a low rotation speed, and the high concentration of Comparative Example 5 was matched with a high rotation speed. Comparative Examples 4 and 5 show that the acid layer thickness deviation increased to ±0.58 μm and ±0.62 μm, respectively, and the TTV deteriorated to 0.47-0.51 μm after acid etching, with uneven etching exhibiting thicker edges or centers. Comparative Example 6 increased the rotation speed to 12 rpm, exceeding the limited range of 5-10 rpm, leading to acid splashing and a further increase in the acid layer thickness deviation to ±0.71 μm. Table 2 indicates that the concentration of organic polychain alcohols and the rotation speed are not independent parameters but rather have a synergistic relationship. Only when the concentration of organic polychain alcohols and the silicon wafer rotation speed are matched according to the rule of "low concentration with high rotation speed, high concentration with low rotation speed" can a uniform acid layer distribution and optimal flatness improvement be obtained.

[0037] Table 2. Verification results of the linkage between different concentrations of organic polychain alcohols and different rotation speeds.

[0038] In some embodiments, before immersing the silicon wafer 21 in the mixed acid solution, the following steps are further included: The silicon wafer 21 is pre-impregnated in a pre-impregnation solution containing organic polychain alcohols, wherein the concentration of the organic polychain alcohols in the pre-impregnation solution is 0.1 to 0.5 times the concentration of the organic polychain alcohols in the mixed acid solution.

[0039] Specifically, after the alkaline etching treatment and before immersing the silicon wafer 21 into the mixed acid solution, the silicon wafer 21 is immersed in a pre-immersion solution containing organic polychain alcohols for pre-immersion treatment. The concentration of the organic polychain alcohols in the pre-immersion solution is 0.1 to 0.5 times the concentration of the organic polychain alcohols in the mixed acid solution. The pre-immersion treatment time is 10 to 30 seconds, so as to form a uniform adsorption layer on the surface of the silicon wafer 21, buffer the violent reaction in the initial stage of subsequent acid etching, suppress the initial reaction peak, and enable the etching of the edge and center of the silicon wafer to start synchronously, further eliminating the over-etching phenomenon at the edge of the silicon wafer.

[0040] Table 3 is a verification table of the pre-wetting treatment effect. In Table 3, in Example 6, the silicon wafer was pre-wetted for 20 seconds in a pre-wetting solution containing organic polychain alcohols (i.e., myristicin) (the volume percentage of organic polychain alcohols was 0.1%, which was 0.25 times the volume percentage of organic polychain alcohols in the mixed acid solution) before acid etching. The results showed that the initial reaction rate dropped to 0.55 μm / s, the difference between the edge etching depth and the center etching depth was only 0.2 μm, and the surface etching uniformity was good. In Comparative Example 7, no pre-wetting was performed, and the silicon wafer was directly placed into the acid bath after alkaline etching treatment. The results showed that the initial reaction rate was as high as 1.8 μm / s, the edge etching depth (9.8 μm) was significantly greater than the center etching depth (7.5 μm), and the etching depth difference reached 2.3 μm, showing obvious edge over-etching. Comparative Example 8 used deionized water for pre-wetting (without organic polychain alcohols); the results showed that although the initial reaction rate (1.2 μm / s) and corrosion depth difference (1.2 μm) were better than Comparative Example 7, they were still significantly worse than Example 6. This indicates that the presence of organic polychain alcohols in the pre-wetting solution plays a crucial role in suppressing the initial reaction peak and achieving uniform corrosion. Therefore, the synergistic use of the pre-wetting step and organic polychain alcohols can effectively buffer the violent reaction in the initial stage of acid corrosion, thereby improving the corrosion uniformity of the silicon wafer edges and center, and further enhancing the overall flatness.

[0041] Table 3 Verification Table of Pre-impregnation Treatment Effect

[0042] In some embodiments, the specific steps of immersing the silicon wafer 21 in the mixed acid solution and simultaneously driving the silicon wafer 21 to rotate further include: Adjust the acid etching parameters to control the etching rate of the mixed acid solution on the silicon wafer 21 to be 5.5 μm / min to 10 μm / min. The acid etching parameters include any one or a combination of two or more of the following: the temperature of the mixed acid solution, the rotation speed of the silicon wafer 21, and the composition of the mixed acid solution.

[0043] Specifically, by using acid etching parameters during the acid etching process, including any one or more of the temperature of the mixed acid solution, the rotation speed of the silicon wafer 21, and the composition of the mixed acid solution (e.g., the volume percentage of the organic polychain alcohol), the etching rate of the mixed acid solution on the silicon wafer 21 is controlled to be 5.5 μm / min to 10 μm / min. This balances the processing efficiency of the silicon wafer with the improvement of the surface flatness of the silicon wafer, avoiding abnormal problems caused by excessively fast or slow etching rates.

[0044] In some embodiments, after immersing the silicon wafer 21 in the mixed acid solution and simultaneously driving the silicon wafer 21 to rotate, the following steps are further included: The silicon wafer 21 is placed in a mixed environment of hydrofluoric acid and ozone for cleaning and drying; The silicon wafer 21 is placed in an ozone oxidation bath for oxidation treatment, and a protective oxide film is generated on the surface of the silicon wafer 21.

[0045] Specifically, after the silicon wafer 21 undergoes acid etching in the acid bath 20, it is placed in a mixed environment of hydrofluoric acid and ozone for cleaning and drying. This thoroughly removes residual acid (e.g., the mixed acid solution), reaction products, metal ions, and trace organic impurities from the surface of the silicon wafer 21, resulting in a clean silicon wafer surface. Subsequently, the silicon wafer 21 is placed in an ozone oxidation bath for oxidation treatment, forming a uniform, dense, and controllable-thickness protective oxide film on its surface. This effectively protects the surface of the silicon wafer 21, preventing damage or contamination during subsequent processing, transportation, or storage.

[0046] The method for improving silicon wafer flatness provided in this specific embodiment involves immersing the polished silicon wafer in a mixed acid solution while simultaneously rotating it. The mixed acid solution includes hydrofluoric acid, nitric acid, and organic polychain alcohols. The organic polychain alcohols constitute 0.4% to 0.6% of the volume of the mixed acid solution, and the rotational speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohols in the mixed acid solution increases. On the one hand, the organic polychain alcohols serve as highly efficient wetting agents and corrosion inhibitors in the acid etching process, enabling the mixed acid solution to form a thick layer on the surface of the silicon wafer. A uniform liquid film layer is formed, and the volume percentage of the organic polychain alcohol in the mixed acid solution is controlled at 0.4%~0.6%, avoiding problems of excessive or insufficient corrosion in certain areas, thus improving the uniformity of acid etching of the silicon wafer. On the other hand, by synergistically controlling the volume percentage of the organic polychain alcohol and the rotation speed of the silicon wafer, the rotation speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohol increases. This enhances the fluidity and uniform coverage of the liquid film while avoiding liquid film fluctuations and splashing, ensuring the stability and controllability of the acid etching process, and achieving synchronous and uniform etching of the entire surface of the silicon wafer. The synergistic effect of the above two aspects effectively improves the flatness of the silicon wafer after polishing, reduces or suppresses the occurrence of edge effects, and achieves effective control of the etching rate. This results in improved flatness of the silicon wafer after wet cleaning; for example, the total thickness change of the silicon wafer after acid etching can be stably reduced to 0.28μm~0.35μm, thereby meeting the requirements of high-end semiconductor devices.

[0047] It should be noted that references to "an embodiment," "an embodiment," "an exemplary embodiment," "some embodiments," etc., in the specification indicate that the described embodiments may include specific features, structures, or characteristics, but each embodiment may not necessarily include that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure, or characteristic is described in connection with an embodiment, whether explicitly described or not, implementing such a feature, structure, or characteristic in conjunction with other embodiments is within the knowledge of those skilled in the art.

[0048] It should be noted that the terms "comprising" and "having," and their variations, used in this invention document are intended to cover non-exclusive inclusion. The terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence, unless explicitly indicated by the context. It should be understood that such data used interchangeably where appropriate. Furthermore, embodiments and features within embodiments of this invention can be combined with each other unless otherwise specified. In addition, descriptions of well-known components and technologies have been omitted in the above description to avoid unnecessarily obscuring the concepts of this invention. In the various embodiments described above, each embodiment focuses on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the flatness of silicon wafers, characterized in that, Includes the following steps: Provide a polished silicon wafer; The silicon wafer is immersed in a mixed acid solution and simultaneously driven to rotate. The mixed acid solution includes hydrofluoric acid, nitric acid, and organic polychain alcohols. The organic polychain alcohols account for 0.4% to 0.6% of the volume percentage of the mixed acid solution, and the rotation speed of the silicon wafer decreases as the volume percentage of the organic polychain alcohols in the mixed acid solution increases.

2. The method for improving silicon wafer flatness according to claim 1, characterized in that, Before immersing the silicon wafer in the mixed acid solution, the following steps are also included: The silicon wafer is cleaned using an ultrasonic cleaning process to remove impurities, including particulate matter, adhering to the surface of the silicon wafer.

3. The method for improving silicon wafer flatness according to claim 2, characterized in that, After cleaning the silicon wafer using ultrasonic cleaning technology, the following steps are also included: The silicon wafer is subjected to alkaline etching treatment in an alkaline bath.

4. The method for improving silicon wafer flatness according to claim 1, characterized in that, The specific steps of immersing the silicon wafer in the mixed acid solution and simultaneously driving the silicon wafer to rotate include: An acid tank containing the mixed acid solution is provided, and the acid tank has a rotating shaft in the middle. The silicon wafer is fixed on the rotating shaft, and the silicon wafer is completely immersed in the mixed acid solution, and the rotating shaft is driven to rotate.

5. The method for improving silicon wafer flatness according to claim 1, characterized in that, The volume ratio of the hydrofluoric acid, the nitric acid and the organic multi-chain alcohol in the mixed acid solution is V 氢氟酸 :V 硝酸 :V 有机多链醇类 =2:197:(0.8~1.2).

6. The method for improving silicon wafer flatness according to claim 4, characterized in that, The specific steps of fixing the silicon wafer to the rotating shaft, ensuring the silicon wafer is completely immersed in the mixed acid solution, and driving the rotating shaft to rotate further include: The temperature of the mixed acid solution in the acid tank is controlled at 20℃±2℃, and the rotation speed of the shaft is controlled at 5rpm~10rpm.

7. The method for improving silicon wafer flatness according to claim 6, characterized in that, The specific steps of fixing the silicon wafer to the rotating shaft, ensuring the silicon wafer is completely immersed in the mixed acid solution, and driving the rotating shaft to rotate further include: Determine whether the volume percentage of the organic polychain alcohol is greater than or equal to 0.4% and less than 0.5%. If so, control the rotation speed of the shaft to 8 rpm to 10 rpm. Determine whether the volume percentage of the organic polychain alcohol is greater than or equal to 0.5% and less than or equal to 0.6%. If so, control the rotation speed of the shaft to 5 rpm to 7 rpm.

8. The method for improving silicon wafer flatness according to claim 1, characterized in that, Before immersing the silicon wafer in the mixed acid solution, the following steps are also included: The silicon wafer is pre-impregnated in a pre-impregnation solution containing organic polychain alcohols, wherein the concentration of the organic polychain alcohols in the pre-impregnation solution is 0.1 to 0.5 times the concentration of the organic polychain alcohols in the mixed acid solution.

9. The method for improving silicon wafer flatness according to claim 1, characterized in that, The specific steps of immersing the silicon wafer in the mixed acid solution and simultaneously driving the silicon wafer to rotate further include: Adjust the acid etching parameters to control the etching rate of the silicon wafer by the mixed acid solution to be 5.5 μm / min to 10 μm / min. The acid etching parameters include any one or a combination of two or more of the following: the temperature of the mixed acid solution, the rotation speed of the silicon wafer, and the composition of the mixed acid solution.

10. The method for improving silicon wafer flatness according to claim 1, characterized in that, After immersing the silicon wafer in the mixed acid solution and simultaneously driving the silicon wafer to rotate, the process further includes the following steps: The silicon wafer was placed in a mixed environment of hydrofluoric acid and ozone for cleaning and drying; The silicon wafer is placed in an ozone oxidation bath for oxidation treatment, and a protective oxide film is generated on the surface of the silicon wafer.

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