A method for electrolytic ultrasonic-assisted cutting of silicon wafers

Abstract

This invention discloses a method for electrolytic ultrasonic-assisted cutting of silicon wafers, which improves wafer quality and efficiency through phased collaborative optimization of the cutting mode. In the initial cutting stage (0-15% depth), a high-voltage EDM mode of 210-250V is used, combined with a feed rate of 2000-2900μm / min and short-cycle wire feeding. This non-contact cutting reduces surface micro-cracks and entry chipping. In the intermediate cutting stage (15-85% depth), the method switches to a low-voltage electrolytic assisted mode of 36-48V, primarily using electrolyte electrochemical corrosion to reduce diamond abrasive wear, fill micro-cracks to achieve uniform peeling, and improve cross-sectional flatness. In the final stage (85-100% depth), ultrasonic-assisted cutting is used. At a low feed rate of 450-860μm / min, ultrasonic vibration causes intermittent separation of abrasive particles, preventing edge chipping and accelerating chip removal to prevent thermal stress cracking. This method, through the superposition of composite cutting technologies, improves cutting efficiency, reduces the surface friction line value of the silicon wafer, and minimizes edge damage.

Description

Technical Field

[0001] This invention relates to the field of silicon rod cutting technology, and in particular to a method for electrolytic ultrasonic-assisted cutting of silicon wafers. Background Technology

[0002] Single-crystal silicon rod cutting is a core process in silicon wafer fabrication in the semiconductor and photovoltaic industries. Its cutting quality directly affects the flatness, thickness uniformity, and lattice integrity of the silicon wafer, thus impacting subsequent chip manufacturing or the photoelectric conversion efficiency of photovoltaic cells. Currently, the industrial sector employs emerging technologies such as wire electrical discharge machining (WEDM), electrolytic cutting, and ultrasonic-assisted wire sawing to improve cutting quality. However, all these methods have significant technical bottlenecks, making it difficult to simultaneously achieve high efficiency, low damage, and process stability.

[0003] In the field of wire electrical discharge machining (EDM), while deionized water as the working medium enables non-contact cutting, it suffers from significant technical drawbacks. Firstly, the high discharge energy leads to a substantial heat-affected zone on the silicon wafer surface. The difference in expansion / contraction rates caused by temperature gradients generates thermal stress within the material, inducing overall warping or localized thickness unevenness, and potentially even lattice slip or microcrack initiation. Secondly, high-energy discharge easily causes abnormal diamond wire breakage, significantly increasing production costs. Furthermore, deionized water cannot effectively suppress the migration of metal impurities. The mixture of cutting chips and metal chips forms a fine-structure adsorption layer on the silicon wafer surface, resulting in residual metal elements and severely impacting the electrical performance of semiconductor devices. This is particularly problematic for large-size ingots with diameters exceeding 150mm. As the cutting depth increases, the dynamic change in the distance between the electrode and the cutting wire makes precise control of the discharge energy difficult, exacerbating issues such as deeper cutting marks, increased stress concentration, and more microcracks. Existing process parameters are ill-suited to the stable processing requirements of large-size silicon ingots.

[0004] Electrolytic cutting technology utilizes the conductivity of an electrolyte to trigger an electrochemical reaction by applying a continuous or pulsed power supply. This, combined with electrochemical passivation or corrosion on top of mechanical grinding, theoretically improves cutting efficiency and surface quality. However, this technology faces multiple challenges in practical applications: the electrolyte needs to maintain a stable residence time at the cutting interface to achieve effective electrochemical reactions. In the initial stages of ingot cutting, due to low debris accumulation and shallow cutting depth, the electrolyte cannot adequately cover the cutting area. As the cutting depth increases, debris accumulation intensifies and the gap size shrinks, significantly reducing electrolyte penetration efficiency and leading to incomplete local electrolysis. More critically, the electrolyte preparation process is complex, and the matching of its concentration ratio, renewal rate, and cutting process parameters (such as table feed speed and diamond wire speed) is difficult to control precisely. This can easily cause abnormally deep cutting textures and failure to achieve the expected cutting rate, ultimately leading to increased cutting rate and increased risk of wire breakage. These factors collectively restrict the widespread application of electrolytic cutting technology in industrial production.

[0005] Ultrasonic-assisted wire sawing technology introduces ultrasonic vibration into traditional diamond wire saw systems, transforming the continuous contact mode between abrasive particles and the workpiece into an intermittent impact mode, theoretically enhancing material removal capacity and improving surface quality. However, this technology has revealed significant engineering challenges in practical applications: ultrasonic vibration must be transmitted to the high-speed moving diamond wire via a guide wheel, and energy attenuation occurs significantly during dynamic transmission, resulting in the actual amplitude acting on the cutting area being far lower than the theoretical design value; the instantaneous tension fluctuations in the diamond wire caused by vibration exceed the compensation range of traditional constant tension systems, increasing the risk of wire breakage and accelerating diamond wire wear due to uncontrollable abrasive wear; furthermore, the structural vibration interference generated by ultrasonic vibration on the cutting equipment significantly shortens its service life and increases maintenance costs. These technical bottlenecks make it difficult to achieve stable, large-scale industrial applications of ultrasonic-assisted cutting.

[0006] Relying solely on novel cutting technologies such as electrical discharge machining (EDM), electrolysis, or ultrasonic assistance is still in its developmental stage and cannot yet meet the demands for efficient and low-damage processing of large-size silicon rods. Although the industry has attempted to combine EDM with electrolysis, or electrolysis with ultrasonic assistance, to improve cutting efficiency and quality, the inherent limitations of each auxiliary method—such as the difficulty in eliminating the heat-affected zone of EDM, insufficient dynamic control precision in the electrolysis process, and severe energy transfer attenuation in ultrasonic vibration—mean that a stable and reliable composite cutting process cannot yet simultaneously achieve a balance between high efficiency, low crack rate, and process stability. There is an urgent need to develop novel composite cutting processes to overcome these current bottlenecks. Summary of the Invention

[0007] This invention proposes a multi-energy-field synergistic silicon rod composite cutting method. By integrating high-voltage electrical discharge machining (EDM), electrolytic-assisted wire sawing, and ultrasonic-assisted cutting technologies, and combining them with a high-precision parameter control system, it dynamically adjusts core process parameters such as electrolytic current, pulse voltage, and ultrasonic amplitude and frequency. This solves the technical difficulties of traditional composite wire sawing, such as excessive heat-affected zone, uneven electrolyte distribution, ultrasonic energy attenuation, and abnormal cutting patterns, achieving efficient and low-damage cutting of large-size silicon rods. The technical solution provided in this application is as follows:

[0008] This application provides a method for electrolytic ultrasonic-assisted cutting of silicon wafers, comprising the following steps:

[0009] Initial cutting stage: The cutting depth of the crystal rod is 0-15%, and a high-voltage electric spark cutting mode with a voltage of 210-250V is adopted; the feed speed of the worktable is controlled between 2000-2900μm / min; the wire feeding and return cycle adopts a small cycle mode, wherein the small cycle is defined as the sum of the single wire feeding amount and the return amount is less than 1200m;

[0010] Intermediate cutting stage: The cutting depth of the crystal rod is 15-85%, and a low-voltage electrolytic assisted cutting mode with a voltage of 36-48V is adopted, mainly using electrolyte-assisted electrochemical corrosion cutting; the feed speed of the worktable is controlled between 1500-1900μm / min; the wire feeding and return cycle also adopts a short cycle mode.

[0011] Final cutting stage: The cutting depth of the crystal rod is 85-100%, and ultrasonic assisted cutting mode is adopted. The feed speed of the worktable is controlled between 450-860μm / min.

[0012] In some specific implementations, in the ultrasonic-assisted cutting mode used in the final cutting stage, the amplitude of the ultrasonic generator is 0.6-0.7μm and the frequency is 25-35kHz.

[0013] In some specific implementations, the high-voltage electric spark cutting mode uses pulsed high voltage, and the duration of the arc discharge pulse is 11-15μs.

[0014] In some specific embodiments, the electrolyte is selected from at least two of the following: hydrofluoric acid, acetic acid, nitric acid, hydrochloric acid, pure water, ethanol, ethylene glycol, potassium hydroxide, sodium hydroxide, fluoride, and sulfide.

[0015] In some specific embodiments, the electrolyte comprises 0.5-1.0% hydrofluoric acid, 2.0-3.5% acetic acid, 1.0-1.5% starch nanocrystals, and the remainder is pure water.

[0016] In some specific implementations, during the intermediate cutting phase, the pulse voltage duration is 30-45 μs.

[0017] In some specific implementations, during the initial cutting stage, the linear speed of the diamond wire is 1000-1500 m / min.

[0018] In some specific embodiments, during the intermediate cutting stage, the linear speed of the diamond wire is 1600-1800 m / min.

[0019] In some specific embodiments, during the final cutting stage, the linear speed of the diamond wire is 1100-1300 m / min.

[0020] In some specific implementations, during the final cutting stage, the wire feeding and return cycle adopts a large cycle mode, wherein the large cycle is defined as the sum of the single wire feeding amount and the return amount being greater than 1400m.

[0021] By adopting the above technical solution, the method for electrolytic ultrasonic-assisted cutting of silicon wafers provided in this application has the following beneficial effects:

[0022] This invention significantly improves silicon wafer cutting quality and efficiency and reduces processing defects through a phased, collaboratively optimized cutting mode: The initial cutting stage employs a 210-250V high-voltage EDM mode combined with a 2000-2900μm / min high feed rate and short-cycle wire feeding. Utilizing the instantaneous high-temperature melting characteristics of the EDM, it overcomes the influence of material hardness, avoiding defects such as severe surface wear, scratches, and insufficient cutting force on the diamond wire. Non-contact cutting effectively reduces surface micro-cracks and chipping at the entry edge. The shallow cutting depth minimizes the temperature gradient in the heat-affected zone, preventing silicon wafer warping and uneven thickness. The intermediate cutting stage employs a 36-48V low-voltage electrolytic auxiliary mode combined with a 1500-1900μm / min medium feed rate and short-cycle wire feeding. The process primarily utilizes electrochemical corrosion to significantly reduce diamond abrasive wear, filling micro-cracks to achieve uniform silicon rod peeling, improving cross-sectional flatness, and avoiding problems such as unstable discharge energy, deep cutting marks, high stress, and numerous micro-cracks caused by high voltage variations with cutting depth. This reduces the risk of wire breakage and the cutting rate. In the final cutting stage, an ultrasonic-assisted mode with a table feed speed of 450-860 μm / min is used. Ultrasonic vibration causes intermittent separation of abrasive particles, preventing material adhesion and edge breakage in the exit area, accelerating chip removal, preventing local thermal stress cracks, and promoting vibration-assisted cutting of accumulated abrasive particles and silicon chips in the final stage. This improves efficiency and avoids cracks caused by particle accumulation. Vibration resets the abrasive particle action position, reducing the final stage marks and improving quality, while also reducing the impact of ultrasound on the equipment and the risk of wire breakage. This invention innovatively integrates three technologies—high-voltage electrical discharge machining (EDM), electrolytic-assisted wire sawing, and ultrasonic-assisted cutting—to construct a composite cutting process system. Coupled with a high-precision parameter control system, it can dynamically adjust core process parameters such as electrolytic current, pulse voltage, and ultrasonic amplitude and frequency. This effectively solves technical challenges in traditional wire sawing, such as excessively large heat-affected zone, uneven electrolyte distribution, ultrasonic energy attenuation, and abnormal cutting patterns. It achieves efficient and low-damage cutting of silicon rods, significantly improving silicon wafer surface quality, cutting efficiency, and yield, while simultaneously reducing production costs and equipment wear. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of an electrolytic ultrasonic-assisted silicon wafer cutting device provided in an embodiment of this application.

[0025] The following is supplementary explanation of the attached figures:

[0026] 10-Pay-out reel; 20-Take-up reel; 30-Carrier; 40-Crystal rod; 50-Power supply; 60-Electrode; 70-Electrolyte; 80-Ultrasonic generator. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0028] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. In the description of this application, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein.

[0029] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0030] This application provides an electrolytic ultrasonic-assisted silicon wafer cutting device, the schematic diagram of which is shown below. Figure 1As shown, the feed reel 10 and take-up reel 20 work together to control the trajectory and tension of the cutting wire; the support body 30 supports the crystal rod 40 to be cut, preventing the crystal rod 40 from shaking or shifting during the cutting process; the power supply 50 provides stable and compliant electrical power; the electrode 60 is closely connected to the power supply 50, and generates discharge and electrochemical reaction after being energized, making it a key component for realizing electrical discharge and electrolytic cutting; the electrolyte 70 acts as a medium for electrochemical corrosion cutting in the intermediate cutting stage, accelerating the cutting process and improving cutting efficiency and quality. This device has a flexible cutting stage switching capability, and can smoothly transition between the initial, intermediate, and final cutting stages according to the cutting process. Specifically, in the initial cutting stage, when the cutting depth of the crystal rod is between 0-15%, the power supply 50 outputs a high voltage of 210-250V, causing the electrode 60 and the crystal rod 40 to form a high-voltage electrical discharge cutting mode. At this time, the carrier 30 drives the worktable of the crystal rod 40 to feed at a speed of 2000-2900μm / min, and the wire feed and return cycle adopts a small cycle mode with the sum of the single wire feed and return amount less than 1200m, thereby quickly penetrating the surface of the crystal rod and starting the cutting operation; entering the intermediate cutting stage, as the cutting depth of the crystal rod reaches 15-85%, the power supply 50 switches to a low voltage of 36-48V, mainly relying on... The cutting process is advanced by an electrochemical corrosion cutting method assisted by electrolyte 70. The feed speed of the worktable is adjusted accordingly to 1500-1900μm / min, and the wire feed and return cycle remains in a small cycle mode to ensure a stable and efficient cutting process. In the final cutting stage, when the ingot cutting depth is 85-100%, the device starts the ultrasonic-assisted cutting mode. The ultrasonic generator 80 generates ultrasonic waves, which are used to finely trim the silicon wafer through the micro-vibration of the ultrasonic waves. At the same time, the feed speed of the worktable is further reduced to 450-860μm / min, ultimately achieving efficient and precise cutting of the silicon wafer and obtaining high-quality silicon wafer products.

[0031] This application provides a method for electrolytic ultrasonic-assisted cutting of silicon wafers, including the following steps:

[0032] Initial cutting stage: The cutting depth of the crystal rod is 0-15%, using a high-voltage EDM cutting mode with a voltage of 210-250V; the table feed speed is controlled between 2000-2900μm / min; the wire feed and return cycle adopts a short cycle mode, where a short cycle is defined as the sum of the single wire feed and return length being less than 1200m. This application uses a 210-250V high-voltage EDM cutting mode in the initial cutting stage, with specific voltage values ​​such as 210V, 215V, 220V, 225V, 230V, 235V, 240V, 245V, and 250V; simultaneously, a large feed speed of 2000-2900μm / min is used, with specific feed speed values ​​such as 2000μm / min, 2100μm / min, 2200μm / min, and 2... Speeds of 300μm / min, 2400μm / min, 2500μm / min, 2600μm / min, 2700μm / min, 2800μm / min, and 2900μm / min are employed. A short-cycle wire feeding method is used to ensure that the sum of the wire fed and returned in a single operation is less than 1200m, with specific totals such as 1000m, 1050m, 1100m, 1120m, 1150m, and 1180m. This stage utilizes the instantaneous high-temperature melting characteristics of electrical discharge machining to effectively overcome the influence of the high-hardness oxide layer or work-hardened layer on the crystal rod surface, avoiding defects such as severe surface wear, scratches, and insufficient cutting force of the diamond wire. The non-contact cutting method reduces surface micro-cracks and chipping at the entry edge. Because of the shallow cutting depth, the temperature gradient in the heat-affected zone of the silicon wafer is small, avoiding inconsistent expansion / contraction rates in different areas of the wafer due to temperature differences. This prevents overall warping or uneven thickness caused by thermal stress. Furthermore, the wires used in the initial stage are all new, with high strength and resistance to breakage, allowing for safe cutting at higher voltages. The electrolyte environment effectively prevents residual metal elements on the silicon wafer surface. In addition, the use of a short-cycle wire feeding mode (unlike the long-cycle mode of over 1400m) combined with a high feed rate of 2000-2900μm / min not only improves cutting efficiency and reduces energy consumption but also ensures normal surface texture on the silicon wafer, avoiding abnormalities such as a rough or uneven feel.

[0033] Intermediate cutting stage: The cutting depth of the crystal rod is between 15-85%, using a low-voltage electrolytic assisted cutting mode of 36-48V, mainly based on electrolyte-assisted electrochemical corrosion cutting; the table feed speed is controlled between 1500-1900μm / min; the wire feed and return cycle also adopts a short cycle mode. This application uses a 36-48V low-voltage electrolytic assisted cutting mode in the intermediate cutting stage, with specific voltage values ​​such as 36V, 37V, 38V, 39V, 40V, 41V, 42V, 43V, 44V, 45V, 46V, 47V, and 48V, coupled with a feed speed of 1500-1900μm / min, with specific feed speed values ​​such as 1500μm / min, 1550μm / min, and 1600μm / min. The speeds are 1650μm / min, 1700μm / min, 1750μm / min, 1800μm / min, 1850μm / min, 1900μm / min, etc., as well as the small-cycle wire feeding mode, where the sum of the single wire feeding amount and the return wire amount is less than 1200m, with specific totals such as 1000m, 1050m, 1100m, 1120m, 1150m, 1180m, etc. As the cutting depth increases from 15% to 85%, the distance between the metal electrode and the cutting line gradually shortens, leading to a rise in voltage. Continuing to use high voltage will result in unstable discharge energy, causing problems such as deep cutting lines, high cutting stress, and numerous microcracks, making precise control difficult. By adopting a low-voltage electrolytic-assisted cutting mode, which mainly uses electrolyte-assisted electrochemical corrosion cutting, diamond abrasive wear can be significantly reduced. Through electrochemical corrosion, microcracks are effectively filled, achieving uniform silicon rod peeling and improving cross-sectional flatness. This effectively reduces the generation of defects such as cracks during the cutting process, making the cutting lines more uniform, reducing stress defects, and ensuring that subsequent silicon wafer texturing, thermal diffusion, and other processes are less prone to cracking and other defects. Using a lower voltage of 36-48V ensures that the voltage change is small as the distance between the metal electrode and the cutting line decreases with increasing cutting depth. This avoids problems such as unstable discharge energy, deeper cutting lines, increased cutting stress, and more microcracks caused by a sharp increase in voltage in high-voltage mode. Low-voltage electrolytic assisted cutting greatly mitigates the adverse effects of voltage changes caused by changes in cutting depth. If the voltage exceeds 48V, not only will there be a risk of electric arc, but the cutting process will also become difficult to control due to changes in cutting depth, resulting in problems such as wider cutting lines, more cutting cracks, increased risk of wire breakage, and increased cutting rate. On the other hand, if the voltage is below 36V, the electrolytic assistance effect is not obvious and cannot effectively improve cutting efficiency.

[0034] Final Cutting Stage: The cutting depth of the crystal rod is 85-100%, using ultrasonic-assisted cutting mode, with the table feed speed controlled between 450-860 μm / min. This application employs a high feed speed of 450-860 μm / min combined with ultrasonic-assisted cutting mode during the final cutting stage. Specific feed speed values ​​include 450 μm / min, 480 μm / min, 500 μm / min, 520 μm / min, 550 μm / min, 580 μm / min, 600 μm / min, 620 μm / min, 650 μm / min, 680 μm / min, 700 μm / min, 720 μm / min, 750 μm / min, 780 μm / min, 800 μm / min, 820 μm / min, 840 μm / min, and 860 μm / min. This technology effectively solves the short circuit problem that may occur at the end of the cutting process due to the connection with the metal electrode, while avoiding the risk of voltage rise caused by the metal electrode being too close to the cutting line. The high-frequency micro-impact anti-adhesion technology causes intermittent separation of the abrasive particles and the silicon wafer by ultrasonic vibration, preventing edge chipping caused by material adhesion in the exit area; vibration accelerates the removal of cutting chips, preventing localized thermal stress cracks caused by chip accumulation at the end; ultrasonic vibration disperses the diamond abrasive particles (such as high-concentration diamond particles generated by wire peeling) and silicon chips accumulated in the final stage, assisting in cutting, improving cutting efficiency, and facilitating the maintenance of a high feed rate, while avoiding cutting cracks caused by localized particle accumulation, further reducing the overcutting rate; vibration periodically resets the position of the abrasive particles, reducing end-stage texture and improving the surface quality of the cut. Furthermore, using ultrasonic-assisted cutting only at the end of the cutting process reduces the impact of the ultrasonic system on the overall equipment and reduces the risk of wire breakage, achieving low-damage final cutting.

[0035] In some specific embodiments, in the ultrasonic-assisted cutting mode used in the final cutting stage, the amplitude of the ultrasonic generator is 0.6-0.7μm and the frequency is 25-35kHz. This application uses a 25-35kHz frequency combined with a 0.6-0.7μm high-frequency micro-amplitude vibration, with specific frequency values ​​such as 25kHz, 26kHz, 27kHz, 28kHz, 29kHz, 30kHz, 31kHz, 32kHz, 33kHz, 34kHz, and 35kHz, corresponding to vibration amplitude values ​​such as 0.60μm, 0.61μm, 0.62μm, 0.63μm, 0.64μm, 0.65μm, 0.66μm, 0.67μm, 0.68μm, 0.69μm, and 0.70μm. Through the precise coordination of high-frequency vibration and micro-amplitude displacement, the cutting resistance is effectively reduced and the surface quality is improved. This intermittent separation of abrasive grains from the silicon wafer surface effectively avoids edge chipping caused by material adhesion in the exit area; ultrasonic vibration accelerates the discharge of cutting chips, preventing localized thermal stress concentration caused by chip accumulation at the end of the cutting process and reducing the risk of thermal stress cracks; the vibration effect keeps the diamond abrasive grains (such as the high concentration of abrasive grains generated by wire stripping) and silicon chips and other impurities accumulated in the final stage in a dynamic dispersion state, avoiding cutting cracks caused by local particle accumulation, and improving material removal efficiency through vibration-assisted cutting.

[0036] In some specific implementations, the high-voltage electrical discharge cutting mode employs pulsed high voltage, with the duration of the arc discharge pulse being 11-15 μs. Specific pulse duration values ​​include 11 μs, 11.2 μs, 11.5 μs, 11.8 μs, 12 μs, 12.2 μs, 12.5 μs, 12.8 μs, 13 μs, 13.2 μs, 13.5 μs, 13.8 μs, 14 μs, 14.2 μs, 14.5 μs, 14.8 μs, and 15 μs. When the arc discharge pulse duration is only 11 μs, the auxiliary effect of the arc discharge is insufficient, leading to insufficient cutting force and easily causing problems such as wire breakage and high cutting rate. It also results in a wider cutting texture, making a smooth cutting effect impossible. Conversely, when the pulse duration exceeds 15 μs, the diamond wire will be continuously subjected to arc impact, increasing the risk of wire breakage and potentially causing interruption during the cutting process. Therefore, by precisely controlling the duration of the arc discharge pulse within the range of 11-15μs, sufficient cutting force can be ensured while avoiding excessive damage to the cutting line, thus achieving a stable and efficient cutting process.

[0037] In some specific embodiments, the electrolyte is selected from at least two of the following: hydrofluoric acid, acetic acid, nitric acid, hydrochloric acid, pure water, ethanol, ethylene glycol, potassium hydroxide, sodium hydroxide, fluoride, and sulfide. The synergistic effect of multiple components can regulate the corrosion rate and selectivity of the electrolyte, effectively balancing the electrochemical corrosion efficiency and surface quality of silicon materials. Mixed solvent systems (such as hydrofluoric acid combined with organic solvents ethanol / ethylene glycol) can optimize electrolyte wettability, promote uniform distribution of electrolyte in the cutting gap, and avoid cutting surface defects caused by uneven local electrolysis. Functional additives (such as fluorides and sulfides) can inhibit side reactions and reduce residual metal ions and microcracks on the silicon wafer surface. Acid-base neutralization systems (such as nitric acid combined with sodium hydroxide) can stabilize the pH value of the electrolyte and prevent instability in the cutting process caused by fluctuations in the acidity or alkalinity of the electrolyte. Through multi-component compounding, the corrosiveness of single strong acid / base electrolytes to equipment can also be reduced, extending the service life of the equipment. At the same time, the protective effect of the electrolyte on the cutting wire can be improved, reducing the risk of abrasive shedding and wire breakage, ultimately achieving a synergistic improvement in silicon wafer surface quality, cutting efficiency, and process stability.

[0038] In some specific embodiments, the electrolyte comprises 0.5-1.0% hydrofluoric acid, 2.0-3.5% acetic acid, and 1.0-1.5% starch nanocrystals, with the remainder being pure water. Maintaining a hydrofluoric acid concentration of 0.5-1.0% and an acetic acid concentration of 2.0-3.5% in the electrolyte effectively accelerates the arc cutting and electrolytic cutting processes. Using a higher proportion of acetic acid not only acts as a corrosion inhibitor, suppressing excessive corrosion of the diamond cutting wire by the strong acidity of hydrofluoric acid, but also prevents the decomposition and destruction of the starch nanocrystals by hydrofluoric acid. Starch nanocrystals, as a widely available and inexpensive nano-additive, possess unique thixotropic properties. They exhibit good fluidity under impact and remain relatively stable when not under stress. This property allows them to maintain excellent fluidity within the wire cutting kerf, effectively carrying away cutting chips and metal scraps, reducing the risk of particles flowing back into the kerf, and thus improving the surface quality of the cut. Furthermore, in the cut area, starch nanocrystals can reduce the fluidity of the electrolyte, slowing down the electrolyte renewal rate in that area and effectively inhibiting excessive electrolytic corrosion. During the arc generation stage, starch nanocrystals partially decompose upon heating, generating carbon and other substances, further enhancing the cutting effect at this stage, achieving a synergistic improvement in cutting efficiency and surface quality.

[0039] In some specific implementations, during the intermediate cutting stage, the pulse voltage duration is 30-45 μs, with specific duration values ​​such as 30 μs, 31 μs, 32 μs, 33 μs, 34 μs, 35 μs, 36 μs, 37 μs, 38 μs, 39 μs, 40 μs, 41 μs, 42 μs, 43 μs, 44 μs, and 45 μs. By generating small-current discharge pulses, defects such as diamond wire breakage and silicon wafer cracking can be effectively prevented, and the discharge repetition frequency can be increased, thereby improving processing speed and achieving a highly efficient and stable cutting process.

[0040] In some specific implementations, the linear speed of the diamond wire is 1000-1500 m / min during the initial cutting stage, with specific values ​​such as 1000 m / min, 1050 m / min, 1100 m / min, 1150 m / min, 1200 m / min, 1250 m / min, 1300 m / min, 1350 m / min, 1400 m / min, 1450 m / min, and 1500 m / min. Increasing the linear speed effectively enhances the cutting force, thereby supporting higher feed rates for efficient cutting.

[0041] In some specific implementations, during the intermediate cutting stage, the linear velocity of the diamond wire is 1600-1800 m / min, with specific values ​​such as 1600 m / min, 1620 m / min, 1640 m / min, 1660 m / min, 1680 m / min, 1700 m / min, 1720 m / min, 1740 m / min, 1760 m / min, 1780 m / min, and 1800 m / min. Increasing the linear velocity effectively enhances the electrolyte renewal rate in the cutting kerf and promotes rapid chip removal, thereby improving cutting quality.

[0042] In some specific implementations, during the final cutting stage, the wire speed of the diamond wire is 1100-1300 m / min, with specific values ​​such as 1100 m / min, 1120 m / min, 1140 m / min, 1160 m / min, 1180 m / min, 1200 m / min, 1220 m / min, 1240 m / min, 1260 m / min, 1280 m / min, and 1300 m / min. This higher wire speed control reduces wire breakage, accelerates cutting efficiency, facilitates chip removal, and minimizes cracking.

[0043] In some specific implementations, during the final cutting stage, the wire feeding and return cycle adopts a large cycle mode, where a large cycle is defined as the sum of the single wire feeding amount and the return amount being greater than 1400m, with specific total values ​​such as 1401m, 1450m, 1500m, 1550m, 1600m, 1650m, 1700m, 1750m, 1800m, etc. By increasing the span of a single wire feed and return, the number of frequent start-stop operations for wire feeding at the end of the cutting process is effectively reduced, thus reducing mechanical wear and electrical system load. The combination of the large cycle mode and ultrasonic-assisted cutting avoids instability in the cutting process caused by wire feeding, ensuring a smooth transition of cutting force at the end stage. Reducing the frequency of high-speed start-stop operations of the wire feeding mechanism helps prevent abnormal vibration of the diamond wire, avoiding micro-cracks and edge chipping defects on the cutting surface. At the same time, this mode matches the lower feed rate requirements at the end stage, optimizes the residence time of the electrolyte in the cutting kerf, promotes more complete chip removal, and prevents secondary cutting damage caused by local accumulation, ultimately achieving a synergistic improvement in cutting quality and equipment life.

[0044] The following detailed description of examples of the present invention is exemplary and is used only to explain the present invention, and should not be construed as limiting the present invention.

[0045] Example 1

[0046] An electrolytic ultrasonic-assisted silicon wafer cutting method comprises the following steps: In the initial cutting stage, the ingot cutting depth is controlled from 0-15%, using a 230V high-voltage electrical discharge cutting mode with an arc discharge pulse duration of 12μs, a table feed speed of 2450μm / min, and a short-cycle wire feed and return cycle of 1100m. The diamond wire speed is 1300m / min. In the intermediate cutting stage, the ingot cutting depth is controlled from 15-85%, using a 42V low-voltage electrolytic assisted cutting mode with a pulse voltage duration of 38μs, a table feed speed of 1600μm / min, and a wire feed... The return cycle continues to use a small cycle mode, with the sum of the single wire feed and return amount being 1100m. The electrolyte composition is 0.7% hydrofluoric acid, 2.8% acetic acid, 1.2% starch nanocrystals, and the remainder pure water. The diamond wire speed is 1750m / min. In the final cutting stage, the crystal rod cutting depth is controlled at 85-100%, and an ultrasonic-assisted cutting mode is adopted. The ultrasonic generator amplitude is 0.6μm and the frequency is 31kHz. The table feed speed is set to 630μm / min. The wire feed and return cycle adopts a large cycle mode, with the sum of the single wire feed and return amount being 1400m. The diamond wire speed is 1250m / min.

[0047] Example 2

[0048] The method for electrolytic ultrasonic-assisted silicon wafer cutting in Example 1 differs in that the duration of the arc discharge pulse is 8 μs.

[0049] Example 3

[0050] The method for electrolytic ultrasonic-assisted silicon wafer cutting, as described in Example 1, differs in that the pulse voltage duration is 62 μs.

[0051] Example 4

[0052] The method for electrolytic ultrasonic-assisted silicon wafer cutting in Example 1 differs in that the electrolyte does not include starch nanocrystals; its composition consists only of 0.5-1.0% hydrofluoric acid and 2.0-3.5% acetic acid, with the remainder being pure water.

[0053] Example 5

[0054] The method for electrolytic ultrasonic-assisted cutting of silicon wafers in Example 1 differs in that the linear speed of the diamond wire is 850 m / min in the initial cutting stage.

[0055] Example 6

[0056] The method for electrolytic ultrasonic-assisted cutting of silicon wafers in Example 1 differs from that the linear speed of the diamond wire is 1250 m / min during the intermediate cutting stage.

[0057] Example 7

[0058] The method for electrolytic ultrasonic-assisted silicon wafer cutting in Example 1 differs in that the linear speed of the diamond wire is 800 m / min during the final cutting stage.

[0059] Comparative Example 1

[0060] Referring to the electrolytic ultrasonic-assisted silicon wafer cutting method of Example 1, the difference is that the initial cutting stage controls the crystal rod cutting depth to 0-15%, and does not use the high-voltage electric spark cutting mode, but is the same as the intermediate cutting stage.

[0061] Comparative Example 2

[0062] Referring to the electrolytic ultrasonic-assisted silicon wafer cutting method in Example 1, the difference is that the cutting depth of the crystal rod is controlled at 85-100% in the final cutting stage, and the ultrasonic-assisted cutting mode is not used, but is the same as the intermediate cutting stage.

[0063] Comparative Example 3

[0064] The method for electrolytic ultrasonic-assisted silicon wafer cutting, as described in Example 1, differs in that a large cycle of 1400m is used throughout the entire cutting process for the sum of the single wire feed and return.

[0065] Test case

[0066] In the slicing experiments of Examples 1-7 and Comparative Examples 1-3, the performance of the silicon wafer dicing process was tested. The test items included TTV value, yield rate, chipping rate, wire breakage rate, microcrack rate (%), and overcut rate (%). The TTV value is used to characterize the uniformity of silicon wafer thickness; the smaller the value, the higher the dicing precision. The yield rate reflects the proportion of qualified slices in the total sample, directly reflecting the overall processing quality level. The chipping rate characterizes the proportion of broken edges of the slices and can assess the process's ability to protect the integrity of the material. The wire breakage rate measures the frequency of wire breakage during processing, directly affecting production stability and efficiency. The microcrack rate (%) characterizes the proportion of microcracks generated inside the silicon wafer. This indicator directly reflects the degree of influence of the dicing process on the internal integrity of the silicon wafer; the lower the microcrack rate, the more effectively the process control can avoid internal damage caused by thermal stress. The overcut rate (%) measures the proportion of additional abnormal dicing phenomena (such as overcutting, abnormal wire marks, etc.) caused by improper process parameters during the dicing process. This indicator reflects the improvement effect of process parameter optimization on the diced surface quality; the lower the overcut rate, the more stable the dicing process and the more the surface quality meets the standard requirements. The characterization results are detailed in Table 1.

[0067] Table 1

[0068]

[0069] Test results show that Example 1 exhibits the best performance across all test indicators, with a TTV value of 6 μm, a pass rate of 98.0%, and chipping, breakage, microcrack, and overcut rates of 0.3%, 5%, 0.3%, and 1.0%, respectively, superior to other examples and comparative examples. Comparative experiments show that adjusting parameters such as arc discharge pulse duration (e.g., Example 2), pulse voltage duration (e.g., Example 3), or electrolyte composition (e.g., Example 4) did not significantly decrease performance, but all slightly reduced the pass rate and increased the chipping or breakage rates. Reducing the diamond wire speed (e.g., Examples 5-7) significantly exacerbated the breakage and overcut rates. In particular, in Example 7, when low-speed wire cutting was used in the final stage, the TTV value rose to 8 μm, the pass rate dropped to 96.0%, and the chipping and overcut rates reached 1.2% and 4.0%, respectively. Comparative Examples 1 and 2, by eliminating the high-voltage EDM cutting in the initial stage and the ultrasonic assistance in the final stage, respectively, resulted in a significant increase in the TTV value to 10 μm, a decrease in the yield to 94.0%, and a simultaneous deterioration in the edge chipping rate and microcrack rate. Comparative Example 3, employing a long-cycle wire feeding mode throughout the process, did not directly affect the edge chipping rate, but the wire breakage rate and overcutting rate increased to 9% and 4.0%, respectively, indicating that optimizing the wire feeding cycle is crucial for process stability. In summary, Example 1, through precise matching of the cutting mode, parameters, and electrolyte formulation in stages, achieved an optimal balance between silicon wafer cutting accuracy, yield, and surface quality.

Claims

1. A method for electrolytic ultrasonic-assisted cutting of silicon wafers, characterized in that, Includes the following steps: Initial cutting stage: The cutting depth of the crystal rod is 0-15%, and a high-voltage electric spark cutting mode with a voltage of 210-250V is adopted; the feed speed of the worktable is controlled between 2000-2900μm / min; the wire feeding and return cycle adopts a small cycle mode, wherein the small cycle is defined as the sum of the single wire feeding amount and the return amount is less than 1200m; Intermediate cutting stage: The cutting depth of the crystal rod is 15-85%, and a low-voltage electrolytic assisted cutting mode with a voltage of 36-48V is adopted, mainly using electrolyte-assisted electrochemical corrosion cutting; the feed speed of the worktable is controlled between 1500-1900μm / min; the wire feeding and return cycle also adopts a short cycle mode. Final cutting stage: The cutting depth of the crystal rod is 85-100%, and ultrasonic assisted cutting mode is adopted. The feed speed of the worktable is controlled between 450-860μm / min.

2. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, In the ultrasonic-assisted cutting mode used in the final cutting stage, the amplitude of the ultrasonic generator is 0.6-0.7μm and the frequency is 25-35kHz.

3. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, The high-voltage electric spark cutting mode uses pulsed high voltage, and the duration of the arc discharge pulse is 11-15μs.

4. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, The electrolyte is selected from at least two of the following: hydrofluoric acid, acetic acid, nitric acid, hydrochloric acid, pure water, ethanol, ethylene glycol, potassium hydroxide, sodium hydroxide, fluoride, and sulfide.

5. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 4, characterized in that, The electrolyte comprises 0.5-1.0% hydrofluoric acid, 2.0-3.5% acetic acid, 1.0-1.5% starch nanocrystals, and the remainder is pure water.

6. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, During the intermediate cutting phase, the pulse voltage duration is 30-45 μs.

7. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, During the initial cutting stage, the linear speed of the diamond wire is 1000-1500 m / min.

8. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, During the intermediate cutting stage, the linear speed of the diamond wire is 1600-1800 m / min.

9. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, During the final cutting stage, the linear speed of the diamond wire is 1100-1300 m / min.

10. The method for electrolytic ultrasonic-assisted cutting of silicon wafers according to claim 1, characterized in that, During the final cutting stage, the wire feeding and return cycle adopts a large cycle mode, wherein the large cycle is defined as the sum of the single wire feeding amount and the return amount being greater than 1400m.

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