A microwave backside reduction processing system and method for a brittle semiconductor wafer

Abstract

The application relates to a microwave back-reducing processing system and method for a hard and brittle semiconductor wafer, which comprises a high-precision numerical control back-reducing grinding machine and a microwave irradiation unit. The numerical control back-reducing grinding machine is provided with two high-precision air floating spindles. The two high-speed air floating spindles are connected with a back-reducing grinding wheel and a workbench through a grinding wheel clamping piece and a workpiece clamping piece, so that self-rotating movement of the grinding wheel and following rotating movement of the semiconductor wafer to be processed are realized. A high-precision linear motor is arranged on the numerical control back-reducing grinding machine. The linear motor is connected with the high-speed air floating spindle connected with the grinding wheel, so that high-precision feeding is realized. The microwave irradiation unit can be combined with the back-reducing grinding wheel processing unit into a microwave-grinding off-axis back-reducing processing system and a microwave-grinding coaxial back-reducing processing system. The microwave back-reducing processing system can realize high-efficiency and ultra-precision "low-temperature" plastic domain grinding processing of the hard and brittle semiconductor wafer.

Description

Technical Field

[0001] This invention relates to the field of ultra-precision machining technology, specifically to a microwave high-efficiency ultra-precision plastic domain back-subtraction machining system and method for hard and brittle semiconductor wafers. Background Technology

[0002] The demand for high-performance semiconductor power devices is increasing in modern industry. Single-crystal silicon carbide (SiC) and gallium nitride (GaN) are typical representatives of third-generation wide-bandgap semiconductor materials. They possess excellent physical properties such as high breakdown electric field, high saturation electron velocity, high thermal conductivity, and strong radiation resistance, which can meet the needs of modern industry for high-power, high-voltage, and high-frequency semiconductor devices. Therefore, they are widely used in modern industrial fields such as aerospace, new energy vehicles, photovoltaic power generation, rail transportation, and smart grids, and have a profound impact on the development of "new infrastructure" in various fields in my country.

[0003] Back-subtraction processing is a crucial step in the manufacturing of high-performance semiconductor power devices. On one hand, it reduces the overall thickness of the chip, facilitating heat dissipation and integration. On the other hand, it reduces the thickness of the damage layer and surface roughness, releasing residual internal stress from previous processing steps and minimizing chip breakage during subsequent dicing. However, SiC and GaN crystals are notoriously difficult to process, leading to rapid wear and failure of ultrafine diamond abrasive wheels during the mechanical removal process. This makes it challenging to achieve efficient and low-cost back-subtraction processing of high-quality SiC and GaN wafers, failing to meet the demands of high-end application markets.

[0004] Therefore, in the research and development of back-thinning processing technology for hard and brittle semiconductor wafers, various external energy fields have been used to assist processing to improve the plastic removal of materials and reduce wafer surface damage and surface roughness. For example, patent CN117381568A proposes a processing device and method for simultaneous thinning of wafers by laser modification. The laser processing system etches and modifies the wafer surface according to the outer edge contour and rotation speed of the grinding wheel, improving the thinning efficiency and reducing the surface roughness, grinding damage, and subsurface damage depth. This patent mainly utilizes the high power and rapid heating effect of the laser to heat the material. As the temperature increases sharply, the material softens, improving its plastic deformation ability and enabling plastic domain processing to achieve improved processing quality. However, the softened material is also more prone to clogging the grinding wheel, which in turn worsens the grinding process and reduces the service life of the grinding wheel. Meanwhile, lasers are sensitive to the surrounding transmission medium. Grinding fluid causes laser refraction and scattering, making it impossible to achieve precise heating and modification of specific areas. In dry grinding, the extremely high temperature in the grinding zone accelerates thermal damage and wear failure of the grinding tool, hindering high-quality and efficient processing. Furthermore, laser heating always proceeds "from the surface inwards," inevitably creating temperature gradients in the material and leading to thermal cracking. In light of this, patent CN207282468U proposes a plasma thinning device that uses highly oxidizing free radicals in plasma to chemically react with the atoms on the workpiece surface, achieving damage-free processing. Due to its unique processing method, the workpiece avoids crystal defects caused by plastic deformation or brittle fracture, and retains its original physical properties. However, the resulting surface modification layer is extremely thin, only a few nanometers, resulting in extremely low processing efficiency (atomic-scale removal rate). Patent CN110625205A proposes a wafer thinning process and apparatus based on the principle of electrical discharge machining (EDM). The wafer serves as the electrode material, and the material is removed by energy generated from the discharge. This method is not limited by material hardness, solving the problem of traditional mechanical grinding for ultrahard materials. Furthermore, EDM is a non-contact process, eliminating contact forces and residual stress, and producing no environmental pollutants. However, the discharge erosion position in EDM is difficult to control precisely, and wafer fragmentation is prone to occur.

[0005] Currently, four common methods for assisted heating cutting of hard and brittle materials are plasma arc, oxyacetylene, laser, and microwave. Plasma arc, oxyacetylene, and laser utilize the Boltzmann thermal effect to rapidly heat the material "from the surface inwards," inevitably leading to a temperature gradient within the material. Since hard and brittle materials are highly sensitive to heat, they are prone to thermal cracking, reducing processing quality. Traditional microwave-assisted heating cutting utilizes the dielectric heating effect of microwaves, using an ultra-high-power microwave generator to simultaneously heat the material from the inside out, significantly shortening heating time and increasing heating efficiency. It can rapidly heat ceramic bulk materials to 1000℃ or even higher, softening the material. However, semiconductor wafers are typically only 300–500 micrometers thick. Excessively high heating temperatures (above 500℃) can cause wafer deformation and severe internal thermal stress, resulting in wafer dimensional accuracy that fails to meet requirements. Furthermore, it easily leads to natural wafer cracking, reducing the yield rate. At the same time, it is still difficult to achieve precise control over heating energy and heating area at this stage, and excessively high temperatures can cause diamond abrasive to carbonize and graphitize, resulting in a significant decrease in strength and reducing the service life of the grinding wheel.

[0006] Furthermore, unlike the microwave dielectric heating effect, patent CN117532089A proposes a method and apparatus for microwave-assisted processing of hard and brittle insulating materials. This method utilizes microwave energy to induce a strong electric field at the processing end of a processing tool, creating a discharge. Subsequently, the electrolyte at the discharge location, affected by the high temperature of the discharge, forms a corrosive electrolyte that chemically etches the workpiece. However, this patent is essentially still a method based on electrochemical processing principles (i.e., utilizing the corrosiveness of the electrolyte) for micro-processing of the surface of insulating ceramic materials, such as creating micropores, fine grooves, and microstructures. It cannot achieve rapid prototyping of large-size, high-quality surfaces. Specifically, this patent is only suitable for the micro-processing of insulating ceramic materials. When the workpiece has conductive or semiconductor properties, the strong electric field generated by the microwave at the processing end will directly erode the conductive workpiece material through discharge (electrical discharge machining principle), making precise control and micro-processing of the workpiece surface impossible. Moreover, it is prone to wafer cleavage when processing large-size semiconductor wafers. Summary of the Invention

[0007] To address the significant contradiction between processing efficiency and quality in the fabrication of difficult-to-machine hard and brittle semiconductor wafers, this invention aims to provide a microwave high-efficiency ultra-precision plastic domain back-reduction processing system and method for hard and brittle semiconductor wafers. This system comprises a microwave module and a grinding module. Unlike existing microwave-assisted processing that utilizes high-frequency, high-power microwaves to heat materials to ultra-high temperatures (1000°C) to improve plasticity, this system primarily utilizes high-frequency, low-power alternating electromagnetic energy from microwaves to directly act on the hard and brittle semiconductor material. The high-frequency alternating electromagnetic energy induces intense collisions and friction between internal atoms, subsequently generating dislocations. Multiplication and slip enhance material plasticity, while the low-power alternating electromagnetic energy output avoids generating excessive heat inside the workpiece. Simultaneously, grinding fluid that does not absorb microwaves (i.e., its temperature does not rise under microwave irradiation) cools and lubricates the abrasive-workpiece interface, reducing thermal damage and wear caused by heat conduction of the grinding wheel. Furthermore, the use of a metal-bonded diamond grinding wheel with microwave-reflecting properties prevents direct heating of the tool material by microwaves, maintaining the high bonding strength and dimensional accuracy of the grinding wheel. Ultimately, this achieves "low-temperature (workpiece temperature below 200°C)" plasticity domain grinding of hard and brittle semiconductor wafers.

[0008] The present invention achieves the above objectives through the following technical solution:

[0009] In a first aspect, the present invention discloses a microwave back-subtraction processing system for hard and brittle semiconductor wafers, comprising a CNC grinding machine and a microwave irradiation unit. The CNC grinding machine is equipped with a first air-bearing spindle and a second air-bearing spindle. The first air-bearing spindle is mounted on a Z-axis moving platform and is driven by a linear motor to achieve feed. The first air-bearing spindle is connected to a grinding wheel processing unit through a grinding wheel clamping device to achieve the self-rotation motion of the grinding wheel processing unit. The second air-bearing spindle is connected to a worktable, which is used to place the hard and brittle semiconductor wafer to be processed, thereby achieving the following rotational motion of the hard and brittle semiconductor wafer to be processed. The microwave irradiation unit is positioned above the hard and brittle semiconductor wafer to be processed, and uses microwave electromagnetic energy to promote the movement of atoms inside the material of the hard and brittle semiconductor wafer to produce slippage, thereby improving plasticity.

[0010] When performing microwave back reduction machining, the microwave irradiation head of the microwave generating component of the microwave irradiation unit is connected to the microwave generator via an antenna; when performing microwave-grinding off-axis back reduction machining, the microwave irradiation head and the liquid spraying device are located on one side of the vacuum self-rotating grinding table, the back reduction grinding wheel machining unit is fixed to the Z-axis movable platform, and the liquid spraying device is used to provide grinding fluid.

[0011] When performing microwave-grinding coaxial back reduction machining, the liquid spraying device is located on one side of the worktable, and the microwave irradiation head of the microwave irradiation unit is installed at the center of the diamond grinding wheel to process hard and brittle semiconductor wafers coaxially with the diamond grinding wheel.

[0012] The working principle of this system is based on the microwave dielectric thermal effect. High-frequency, low-power microwaves directly irradiate the surface of hard and brittle semiconductor materials. The high-frequency alternating electromagnetic energy induces collisions and friction between atoms inside the crystal material, resulting in dislocation multiplication and slip, thereby improving the material's plasticity. Meanwhile, the low-power alternating electromagnetic energy output avoids generating a large amount of heat inside the material. At the same time, grinding fluid that does not absorb microwaves is used to cool and lubricate the abrasive-workpiece contact interface, reducing thermal damage and wear of the grinding wheel caused by heat conduction. Furthermore, the use of a metal-bonded diamond grinding wheel that does not absorb microwaves avoids direct heating of the tool material by microwaves, maintaining the high bonding strength and dimensional accuracy of the grinding wheel. Ultimately, this achieves "low-temperature" plasticity domain grinding of hard and brittle semiconductor wafers.

[0013] As a further technical solution, the microwave irradiation unit and the grinding wheel processing unit are coaxially arranged. The microwave irradiation head of the microwave irradiation unit is connected to the microwave generator via a microwave antenna, and the microwave irradiation head is placed at the center of the ultrafine diamond abrasive wheel. The liquid spraying device is offset from the ultrafine diamond abrasive wheel. Through the interaction of microwaves and the grinding wheel, combined with the cooling, lubrication, and rinsing effects of the grinding fluid, microwave-grinding coaxial back-reduction processing is performed on the hard and brittle semiconductor wafer.

[0014] As a further technical solution, the microwave irradiation head and liquid spraying device of the microwave irradiation unit are biased onto the ultrafine diamond abrasive wheel; through the cooperation of microwave and grinding wheel, combined with the cooling, lubrication and rinsing effects of grinding fluid, microwave-grinding off-axis back reduction processing is performed on hard and brittle semiconductor wafers.

[0015] As a further technical solution, the grinding fluid does not contain polar molecules and is a type of lubricant that does not absorb microwaves (i.e., it will not be heated by microwaves and can maintain excellent cooling performance).

[0016] As a further technical solution, the grinding wheel processing unit is an ultrafine diamond abrasive grinding wheel, which is a metal-bonded diamond abrasive grinding wheel. Therefore, it will not absorb microwaves (i.e., it will not be heated by microwaves and can maintain high bonding strength), and its abrasive particle size is 0.5 to 5 micrometers.

[0017] The microwave back-subtraction machining in this invention mainly utilizes microwave electromagnetic energy to promote the propagation and slippage of dislocations inside brittle crystalline materials, thereby improving plastic deformation capacity and achieving efficient and high-quality machining.

[0018] Secondly, the present invention relates to a processing method based on the aforementioned coaxial arrangement of the microwave irradiation unit and the grinding wheel processing unit, as follows:

[0019] The processed hard and brittle semiconductor wafer is fixed onto the worktable;

[0020] Move the grinding fluid spraying device to the side of the hard and brittle semiconductor wafer to be processed;

[0021] The non-microwave-absorbing grinding fluid is evenly sprayed onto the surface of the hard and brittle semiconductor wafer to be processed through a spraying device.

[0022] The worktable rotates the hard and brittle semiconductor wafer to be processed.

[0023] The microwave irradiation head is connected to the microwave generator via a microwave antenna, placed in the center of the grinding unit and fixed in parallel. Then it is installed on the Z-axis movable platform, and the Z-axis is moved for tool setting.

[0024] The microwave generator adjusts the microwave emission power to radiate microwaves; the grinding wheel processing unit performs grinding.

[0025] After processing is complete, turn off the microwave generator and turn off the vacuum self-rotating grinding table to retract the tool to a safe position.

[0026] As a further technical solution, the critical cutting depth d of hard and brittle semiconductor wafers c =λ(H / E) 1 / 2 (K c / H) 2 In the formula, λ (approximately 8.7) is the brittle-to-plastic transition factor of the hard-brittle semiconductor wafer material, H is the hardness of the hard-brittle semiconductor wafer material after microwave irradiation, E is the elastic modulus of the hard-brittle semiconductor wafer material after microwave irradiation, and K... c It refers to the fracture toughness of hard and brittle semiconductor wafer materials after microwave radiation.

[0027] Secondly, based on the aforementioned microwave irradiation unit being located on one side of the grinding wheel processing unit and positioned on different axes, the corresponding processing methods are as follows:

[0028] The processed hard and brittle semiconductor wafers are mounted onto the worktable;

[0029] Place the microwave irradiation head on one side of the hard and brittle semiconductor wafer to be processed, and determine the relative position of the microwave irradiation head and the surface of the hard and brittle semiconductor wafer;

[0030] Move the spray head of the grinding fluid spraying device to the side of the hard and brittle semiconductor wafer to be processed;

[0031] The grinding fluid that does not absorb microwaves is evenly sprayed onto the surface of the hard and brittle semiconductor wafer to be processed through a micro-lubricant spraying device.

[0032] A microwave generator performs microwave radiation to perform "low-temperature" plastic modification on the surface material of the hard and brittle semiconductor wafer to be processed, adjusting the microwave heating position and the size of the microwave irradiation area;

[0033] The worktable drives the hard and brittle semiconductor wafers to rotate;

[0034] The grinding wheel processing unit is installed on the Z-axis movable platform of the machine tool, and the Z-axis is moved to perform tool setting and grinding.

[0035] After processing is complete, turn off the microwave generator and the vacuum self-rotating grinding table, retract the tool to a safe position, and simultaneously return the microwave generator to a safe position.

[0036] As a further technical solution, the critical cutting depth d of hard and brittle semiconductor wafers c =λ(H / E) 1 / 2 (K c / H) 2 In the formula, λ (approximately 8.7) is the brittle-to-plastic transition factor of the hard-brittle semiconductor wafer material, H is the hardness of the hard-brittle semiconductor wafer material after microwave irradiation, E is the elastic modulus of the hard-brittle semiconductor wafer material after microwave irradiation, and K... c It refers to the fracture toughness of hard and brittle semiconductor wafer materials after microwave radiation.

[0037] As a further technical solution, the microwave radiation area is the working area of ​​the grinding wheel processing unit.

[0038] The beneficial effects of this invention are as follows:

[0039] The processing system of this invention is a detachable microwave back-reduction processing system, which is easy to integrate. The microwave irradiation unit can be combined with the back-reduction grinding wheel processing unit to form a microwave-grinding off-axis back-reduction processing system and a microwave-grinding coaxial back-reduction processing system. At the same time, when performing microwave back-reduction processing on semiconductor wafers, this invention uses high-frequency alternating electromagnetic energy to induce collisions and friction between atoms inside the crystal, promoting the propagation and slippage of dislocations, thereby improving the plastic deformation capacity. The low-power alternating electromagnetic energy output can avoid the material generating a large amount of heat. Meanwhile, the grinding fluid that does not absorb microwaves is used to cool and lubricate the abrasive-workpiece contact interface, reducing thermal damage and wear of the grinding wheel caused by heat conduction. Furthermore, the use of a metal-bonded diamond grinding wheel that does not absorb microwaves avoids direct heating of the tool material by microwaves, maintaining the high bonding strength and dimensional accuracy of the grinding wheel, and achieving high-efficiency, high-quality, and "low-temperature" plastic domain grinding processing. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0041] Figure 1 , Figure 2 These are schematic diagrams of the microwave-grinding off-axis back reduction machining system and the microwave-grinding off-axis back reduction machining system of the present invention, respectively.

[0042] Figures 3(a), 3(b), and 3(c) are schematic diagrams of the microwave irradiation unit, the liquid spraying device, and the grinding wheel processing unit of the present invention, respectively.

[0043] Figure 4(a) is a simplified schematic diagram of the microwave-grinding off-axis back reduction machining system;

[0044] Figure 4(b) is a simplified schematic diagram of the microwave-grinding coaxial back reduction machining system;

[0045] Among them, 1-CNC machine tool, 2-high-speed air-bearing spindle, 3-vacuum self-rotating grinding table, 4-hard and brittle semiconductor wafer, 5-multi-degree-of-freedom magnetic clamp, 6-Z-axis moving platform, 7-microwave irradiation unit, 8-spraying device, 9-grinding wheel processing unit, 10-microwave-grinding off-axis back reduction processing system, 11-microwave-grinding coaxial back reduction processing system; Detailed Implementation

[0046] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0048] With the rapid development of the power electronics industry, the performance requirements of semiconductor devices are gradually increasing. Wafer thinning technology plays an important role in semiconductor chip manufacturing. On the one hand, thinning can reduce the overall thickness of the chip, which is beneficial for heat dissipation and integration; on the other hand, it can reduce the thickness of the damage layer and surface roughness on the wafer surface, release the internal stress accumulated inside the wafer caused by previous processes, and reduce the degree of chip breakage during dicing. Currently, wafer thinning research and development is still in the research and development stage and cannot meet the requirements of high-end applications. Therefore, this embodiment provides a microwave high-efficiency ultra-precision plastic domain back-subtraction processing system and method for hard and brittle semiconductor wafers.

[0049] Generally, the main way to improve the plasticity of materials is through heating. Heating the material promotes molecular movement and slippage within the material, thereby increasing its plasticity. Laser-assisted machining is a commonly used auxiliary method in processing. While it can achieve good surface quality, its drawbacks cannot be ignored. Due to the lack of lubrication and cooling from grinding fluid or cutting fluid, the tool or grinding wheel cannot be cooled, leading to a reduction in tool or wheel life. Lasers, based on the Boltzmann thermal effect, heat is always transferred from the surface inwards, inevitably creating a temperature gradient and making the material prone to thermal cracking. In contrast, microwave electromagnetic energy directly acts on the polar molecules or ions within the material, inducing slippage to improve plasticity. Heat is merely a byproduct of the interaction between microwave energy and the material. Therefore, compared to lasers, microwave back-subtraction machining can perform plastic processing at "low temperatures." Furthermore, the grinding fluid in this invention is a type of cooling and lubricating fluid that does not absorb microwaves. It is not heated by microwaves to generate high temperatures, thus cooling and lubricating the abrasive-workpiece interface during the processing of hard and brittle semiconductor wafers, reducing thermal damage and wear caused by heat conduction of the grinding wheel. Moreover, the non-microwave-absorbing grinding fluid does not affect the microwave irradiation path, allowing for precise irradiation of specific areas. This enables fine control of the plastic deformation of the hard and brittle semiconductor wafer. By adjusting the microwave power and processing time, the degree of plastic deformation and the amount of plastic removal can be precisely controlled. Simultaneously, the use of a non-microwave-absorbing metal-bonded diamond grinding wheel avoids direct heating of the tool material by microwaves, maintaining the high bonding strength and dimensional accuracy of the grinding wheel, achieving high-efficiency, high-quality, and "low-temperature" plastic zone grinding.

[0050] Glossary: ​​In this invention, "low temperature" refers to a workpiece temperature below 200°C;

[0051] Example 1

[0052] This embodiment provides a microwave high-efficiency ultra-precision plastic domain back-subtraction processing system and method for hard and brittle semiconductor wafers, such as... Figure 1 As shown. The microwave high-efficiency ultra-precision plastic domain back reduction machining system for hard and brittle semiconductor wafers includes a high-precision CNC back reduction grinding machine 1, a microwave irradiation unit 7, and a liquid spraying device 8. The CNC back reduction grinding machine 1 is equipped with two high-precision air-bearing spindles 2. The two high-speed air-bearing spindles are connected to the back reduction grinding wheel and the vacuum self-rotating grinding table 3 through the grinding wheel clamping device and the workpiece clamping device, respectively, to realize the self-rotation motion of the grinding wheel and the output motion of the vacuum self-rotating grinding table 3 around its own axis. The vacuum self-rotating grinding table 3 adopts the existing vacuum adsorption hard and brittle semiconductor wafer, and its specific structure is not described in detail here. A high-precision linear motor is mounted on the bed of the CNC back reduction grinding machine. The linear motor is connected to the high-speed air-bearing spindle connected to the grinding wheel to realize high-precision feed. The bed of the CNC machine tool 1 is also equipped with a Z-axis moving platform 6, which can output vertical motion (according to Figure 1The orientation shown is the horizontal movement direction, and the output movement direction is parallel to the axis direction of the high-speed air-bearing spindle 2; the spraying device 8 and the grinding wheel processing unit 9 are detachably connected to the Z-axis moving platform 6.

[0053] The microwave irradiation unit 7 is held on the left side of the hard and brittle semiconductor wafer to be processed by a multi-degree-of-freedom magnetic clamp. The microwave irradiation unit 7 and the grinding wheel processing unit 9 are not coaxially arranged, that is, the microwave irradiation unit 7 and the grinding wheel processing unit 9 can be combined to form a microwave-grinding off-axis back-reduction machining system. The microwave irradiation head in the microwave irradiation unit 7 is connected to a microwave generator, and the microwave energy generated by the microwave generator can be emitted to the hard and brittle semiconductor wafer to be processed through the microwave irradiation head. The liquid spraying device 8 can uniformly spray the grinding fluid that does not absorb microwaves required during the processing. Sprinkled onto the surface of the hard and brittle semiconductor wafer to be processed; the grinding wheel processing unit 9 includes a grinding power system, a high-speed air-bearing spindle, a grinding wheel fixture, etc. The grinding power system can output rotational motion and is connected to the high-speed air-bearing spindle. A grinding wheel fixture is set on the high-speed air-bearing spindle, and a grinding wheel is connected to the grinding wheel fixture. The grinding wheel is a diamond grinding wheel with an abrasive particle size of 0.5 to 5 μm. The distance between the diamond grinding wheel and the biased microwave irradiation head is selected from 1.0 to 10.0 cm, and the effective microwave radiation area diameter is 50 mm.

[0054] In this embodiment, the microwave generator in the microwave irradiation unit 7 has a microwave irradiation head power of 100W, an output power of 0W to 100W, and a frequency of 2450MHz.

[0055] During processing, this invention utilizes the microwave dielectric heating effect, where high-frequency, low-power microwaves directly irradiate the surface of hard and brittle semiconductor materials. The high-frequency alternating electromagnetic energy induces collisions and friction between atoms within the crystal material, resulting in dislocation multiplication and slip, thereby improving the material's plasticity. The low-power alternating electromagnetic energy output avoids generating excessive heat within the material. Simultaneously, grinding fluid that does not absorb microwaves cools and lubricates the abrasive-workpiece interface, reducing thermal damage and wear caused by heat conduction in the grinding wheel. Furthermore, the use of a metal-bonded diamond grinding wheel that does not absorb microwaves prevents direct heating of the tool material by microwaves, maintaining the high bonding strength and dimensional accuracy of the grinding wheel. Ultimately, this invention achieves "low-temperature" plastic grinding of hard and brittle semiconductor wafers, as well as economical, efficient, and near-destructive ultra-precision machining.

[0056] As a further technical solution, the hard and brittle semiconductor wafer to be processed is vacuum adsorbed in front of the vacuum self-selecting rotary grinding table, and then placed in anhydrous ethanol for ultrasonic cleaning for a set time to remove contaminants from the surface of the hard and brittle semiconductor wafer.

[0057] As a further technical solution, the distance between the diamond grinding wheel and the offset microwave irradiation head is selected within the range of 1.0 to 10.0 cm, and the microwave radiation area is the working area of ​​the diamond grinding wheel.

[0058] As a further technical solution, the equipment is equipped with a protective cover to resist microwave interference, which enables it to operate normally during microwave back-subtraction processing.

[0059] It should be noted that the microwave action of this system avoids generating a large amount of heat. It mainly utilizes microwave energy to interact with the atoms inside the hard and brittle semiconductor wafer to promote dislocation multiplication and slip, thereby improving plasticity.

[0060] Using this system, the specific steps for microwave-grinding off-axis back-reduction machining of hard and brittle semiconductor wafers are as follows:

[0061] S1: Vacuum adsorption of the hard and brittle semiconductor wafer after ultrasonic cleaning onto the vacuum self-rotating grinding stage;

[0062] S2: Hold the microwave irradiation head in a multi-degree-of-freedom magnetic clamp and place it on the left side of the hard and brittle semiconductor wafer to be processed. Determine the relative position between the microwave irradiation head and the surface of the hard and brittle semiconductor wafer. Install the spraying device on the Z-axis movable platform and move the nozzle to the left side of the hard and brittle semiconductor wafer to be processed.

[0063] S3: The grinding fluid that does not absorb microwaves is evenly sprayed onto the surface of the hard and brittle semiconductor wafer through a spraying device.

[0064] S4: Turn on the microwave generator to perform microwave radiation, and perform "low-temperature" plastic modification on the surface material of hard and brittle semiconductor wafers. Adjust the position and size of the microwave irradiation area using a multi-degree-of-freedom magnetic fixture.

[0065] S5: Turn on the vacuum self-rotating grinding stage to drive the hard and brittle semiconductor wafer to rotate;

[0066] S6: Install the back reduction grinding wheel machining unit onto the machine tool's Z-axis movable platform and move the Z-axis to perform tool setting;

[0067] S7: Start the CNC machine tool and perform microwave-grinding off-axis back reduction machining on the hard and brittle semiconductor wafer. After the machining is completed, turn off the microwave generator and the vacuum self-rotating grinding table, retract the tool to the safe position, and at the same time, withdraw the microwave generator to the safe position.

[0068] The method for fabricating gallium nitride wafers using this system and method is as follows:

[0069] S1: Place the gallium nitride wafer in anhydrous ethanol and ultrasonically clean it for 10 minutes to obtain a clean and uncontaminated gallium nitride wafer;

[0070] S2: Use a digital display heating instrument to fix the hard and brittle semiconductor wafer to be processed onto the aluminum alloy sample stage with paraffin wax. Start the silent oil-free vacuum pump and vacuum adsorb the aluminum alloy sample stage onto the machine tool's vacuum self-rotating grinding table. Adjust the spindle rotation accuracy to less than 1μm using a high-precision dial indicator.

[0071] S3: Install the microwave irradiation head on the multi-degree-of-freedom magnetic chuck, attach the multi-degree-of-freedom magnetic chuck to the left side of the vacuum self-rotating grinding table, adjust the multi-degree-of-freedom magnetic chuck to move the microwave irradiation head to the left side of the gallium nitride wafer to be processed, and determine its relative position to the surface of the gallium nitride wafer.

[0072] S4: Start the high-precision CNC machine tool 1, turn on the control system, control the moving mechanism to move the diamond grinding wheel above the gallium nitride wafer, adjust the relative position of the grinding wheel and the surface of the gallium nitride wafer by controlling the moving mechanism and the air-bearing spindle, and read the coordinate value of the Z coordinate system of the tool machine tool.

[0073] S5: Set the microwave processing parameters, turn on the microwave generator to irradiate the gallium nitride wafer processing area, and uniformly spray non-microwave-absorbing grinding fluid onto the gallium nitride wafer surface at a flow rate of 50L / h using a spraying device. The grinding fluid is used for cooling and lubrication, while simultaneously using microwave energy to perform "low-temperature" plastic modification on the gallium nitride wafer. The size of the microwave radiation area is adjusted using a multi-degree-of-freedom magnetic chuck.

[0074] S6: Start the high-speed air-bearing spindle 2, so that the vacuum self-rotating grinding table carries the gallium nitride wafer to rotate;

[0075] S7: Start the high-speed air-bearing spindle and air-bearing spindle assembly, control the Z-axis to feed 0.5μm at a time for trial grinding, until the center of the ground sample is flat and free of micro-protrusions, and complete the tool setting;

[0076] S8: Turn on the microwave generator and irradiate a specific location on the gallium nitride wafer with microwaves. Use an infrared thermal imager to observe the surface of the gallium nitride wafer immediately after microwave irradiation. Select the location of the microwave irradiation head corresponding to the hot spot with good roundness and uniform energy, and finally determine the microwave working position.

[0077] S9: The microwave irradiation head is tilted 30 degrees relative to the diamond grinding wheel using a multi-degree-of-freedom magnetic clamp, ensuring the center of the hot spot on the gallium nitride wafer surface is concentric with the center of the diamond grinding wheel. Grinding parameters are set as follows: gallium nitride wafer rotation speed 1000 rpm, grinding wheel rotation speed 3000 rpm, grinding depth DOC 0.5 μm, feed rate 1 μm / min. Microwave parameters are set as follows: microwave action area diameter 50 mm, power 50 W, time 30 min.

[0078] S10: Start the high-precision CNC machine tool and begin microwave-assisted wafer thinning of the gallium nitride wafer. After processing is complete, retract the tool to a safe position;

[0079] S11: Retract the microwave irradiation head to a safe position and shut down the microwave generator, high-speed air-bearing spindle and air-bearing spindle assembly, control system and cooling and lubrication system.

[0080] Example 2

[0081] This embodiment provides another microwave back-subtraction machining system, which differs from Embodiment 1 in that the microwave irradiation unit 7 can be coaxially arranged with the grinding wheel machining unit 9, i.e., it is combined into a microwave-grinding coaxial back-subtraction machining system. Specifically, in this embodiment, the diamond grinding wheel and the grinding wheel fixture are hollow. The microwave irradiation head of the microwave irradiation unit 7 is placed in the center of the diamond grinding wheel and fixed inside the grinding wheel fixture. The microwave generator is installed on the Z-axis moving platform. The microwave antenna connected to the microwave generator passes through the high-speed air-bearing spindle of the grinding wheel, the grinding wheel fixture, and is connected to the microwave irradiation head. The grinding power system can output rotational motion. The grinding power system is connected to the high-speed air-bearing spindle. The grinding wheel fixture is provided on the high-speed air-bearing spindle. The grinding wheel fixture is connected to the grinding wheel and the microwave irradiation head. The rest of the structure is the same as that in Embodiment 1, and will not be described in detail here.

[0082] Using this system, the method for microwave-grinding coaxial back-subtraction machining of hard and brittle semiconductor wafers is as follows:

[0083] S1: Vacuum adsorption of the hard and brittle semiconductor wafer after ultrasonic cleaning onto the vacuum self-rotating grinding stage;

[0084] S2: Install the spraying device on the Z-axis movable platform and move the nozzle to the left side of the hard and brittle semiconductor wafer to be processed;

[0085] S3: The grinding fluid that does not absorb microwaves is evenly sprayed onto the surface of the hard and brittle semiconductor wafer through a spraying device.

[0086] S4: Turn on the vacuum self-rotating grinding stage to drive the hard and brittle semiconductor wafer to rotate;

[0087] S5: Connect the microwave irradiation head to the microwave generator via the microwave antenna, place it at the center of the diamond grinding wheel, fix it using the grinding wheel clamp, install it onto the machine tool's Z-axis movable platform, and move the Z-axis for tool setting;

[0088] S6: Turn on the microwave generator, adjust the microwave emission power to radiate microwaves, start the CNC machine tool, and perform microwave-grinding coaxial back reduction machining on the hard and brittle semiconductor wafer. After the machining is completed, turn off the microwave generator and turn off the vacuum self-rotating grinding table to retract the tool to a safe position.

[0089] As a further technical solution, in microwave-grinding coaxial back reduction machining, the diamond grinding wheel and grinding wheel fixture are hollow, the microwave irradiation head is placed in the center of the diamond grinding wheel and fixed inside the grinding wheel fixture, the distance between the microwave irradiation head and the processing surface of the hard and brittle semiconductor wafer is 1cm, and the microwave radiation area is the working area of ​​the diamond grinding wheel.

[0090] The method for microwave back-subtraction processing of gallium nitride wafers specifically includes the following steps:

[0091] S1: Place the gallium nitride wafer in anhydrous ethanol and ultrasonically clean it for 10 minutes to obtain a clean and uncontaminated gallium nitride wafer;

[0092] S2: Use a digital display heating instrument to fix the hard and brittle semiconductor wafer to be processed onto the aluminum alloy sample stage with paraffin wax. Start the silent oil-free vacuum pump and vacuum adsorb the aluminum alloy sample stage onto the machine tool's vacuum self-rotating grinding table. Adjust the spindle rotation accuracy to less than 1μm using a high-precision dial indicator.

[0093] S3: Connect the microwave irradiation head to the microwave generator via the microwave antenna, place it at the center of the diamond grinding wheel, and fix it using the grinding wheel clamp. Then install the grinding wheel processing unit and the microwave generator onto the machine tool's Z-axis movable platform.

[0094] S4: Start the high-precision CNC machine tool 1, turn on the control system, control the moving mechanism to move the diamond grinding wheel above the gallium nitride wafer, adjust the relative position of the grinding wheel and the surface of the gallium nitride wafer by controlling the moving mechanism and the air-bearing spindle, and read the coordinate value of the Z coordinate system of the tool machine tool.

[0095] S5: Set the microwave processing parameters, turn on the microwave generator to radiate the gallium nitride wafer processing position, and spray the non-microwave-absorbing grinding fluid evenly onto the surface of the gallium nitride wafer through the spraying device at a flow rate of 50L / h. The grinding fluid is used for cooling and lubrication, and at the same time, the microwave energy is used to perform "low-temperature" plastic modification on the gallium nitride wafer.

[0096] S6: Start the high-speed air-bearing spindle 2, so that the vacuum self-rotating grinding table carries the gallium nitride wafer to rotate;

[0097] S7: Start the high-speed air-bearing spindle and air-bearing spindle assembly, control the Z-axis to feed 0.5μm per cycle until the center of the ground sample is flat and free of micro-protrusions, and complete the tool setting;

[0098] S8: Turn on the microwave generator to irradiate the gallium nitride wafer with microwaves, and use an infrared thermal imager to observe the surface of the gallium nitride wafer immediately after microwave irradiation.

[0099] S9: The center of the hot spot on the gallium nitride wafer surface irradiated by microwave is concentric with the center of the diamond grinding wheel. Grinding parameters are set as follows: gallium nitride wafer rotation speed 1000 rpm, grinding wheel rotation speed 3000 rpm, grinding depth DOC 0.5 μm, feed rate 1 μm / min. Microwave parameters are set as follows: microwave action area diameter 50 mm, power 50 W, time 30 min.

[0100] S10: Start the high-precision CNC machine tool and begin microwave coaxial-assisted wafer thinning of the gallium nitride wafer. After processing is complete, retract the tool to a safe position;

[0101] S11: Shut down the microwave generator, high-speed air-bearing spindle and air-bearing spindle assembly, control system and cooling and lubrication system.

[0102] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A microwave back-subtraction processing system for hard and brittle semiconductor wafers, characterized in that: The system includes a CNC grinding machine, a microwave irradiation unit, a grinding fluid spraying device, and a grinding wheel processing unit. The CNC grinding machine is equipped with a first air-bearing spindle and a second air-bearing spindle. The first air-bearing spindle is mounted on a Z-axis moving platform and is driven by a linear motor for feed. The first air-bearing spindle is connected to the grinding wheel processing unit via a grinding wheel clamping device, enabling the grinding wheel processing unit to rotate. The second air-bearing spindle is connected to a worktable, which holds the hard and brittle semiconductor wafer to be processed, allowing the wafer to follow its rotation. The microwave irradiation unit is positioned above the hard and brittle semiconductor wafer. A microwave irradiation head within the unit is connected to a microwave generator, and the microwave energy generated by the generator is emitted through the irradiation head to the wafer. The process involves using microwave electromagnetic energy to promote the proliferation and slippage of dislocations within the hard and brittle semiconductor wafer material through collisions and friction. High-frequency, low-power alternating electromagnetic energy directly acts on the hard and brittle semiconductor material, inducing intense collisions and friction between internal atoms, leading to dislocation proliferation and slippage, thus improving material plasticity. The low-power alternating electromagnetic energy output avoids generating excessive heat within the workpiece. The grinding fluid spraying device is positioned obliquely above the hard and brittle semiconductor wafer. The grinding fluid contains no polar molecules and is a type of lubricant that does not absorb microwaves. The grinding wheel processing unit is an ultrafine diamond abrasive wheel, a metal-bonded diamond abrasive wheel that does not absorb microwaves. The microwave radiation area is the effective area of ​​the grinding wheel processing unit, and the diameter of the effective microwave radiation area is 50 mm. The microwave irradiation unit has a microwave generator with a microwave irradiation head power of 100 W, an output power of 0 W to 100 W, and a frequency of 2450 MHz.

2. The microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 1, characterized in that: The microwave irradiation unit is coaxially arranged with the grinding wheel processing unit. The microwave irradiation head of the microwave irradiation unit is connected to the microwave generator through a microwave antenna, and the microwave irradiation head is placed at the center of the grinding wheel processing unit.

3. The microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 1, characterized in that: The microwave irradiation head and liquid spraying device of the microwave irradiation unit are offset on the ultrafine diamond abrasive wheel.

4. The microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 1, characterized in that: The abrasive particle size of the metal-bonded diamond abrasive wheel is 0.5~5 micrometers.

5. The processing method of the microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 2, characterized in that: The processed hard and brittle semiconductor wafer is fixed onto the worktable; The non-microwave-absorbing grinding fluid is evenly sprayed onto the surface of the hard and brittle semiconductor wafer to be processed through a spraying device. The worktable rotates the hard and brittle semiconductor wafer to be processed. The microwave irradiation head is connected to the microwave generator via a microwave antenna, placed in the center of the grinding wheel processing unit and fixed. Then it is installed on the Z-axis movable platform, and the Z-axis is moved for tool setting. The microwave generator adjusts the microwave emission power to radiate microwaves; the grinding wheel processing unit performs grinding. After processing is complete, turn off the microwave generator and turn off the vacuum self-rotating grinding table to retract the tool to a safe position.

6. The processing method of the microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 5, characterized in that: Critical cutting depth of hard and brittle semiconductor wafers d c = λ ( H / E ) 1 / 2 ( K c / H) 2 In the formula λ It is the brittle-plastic transition factor for hard and brittle semiconductor wafer materials. H It refers to the hardness of brittle semiconductor wafer materials after microwave radiation. E It is the elastic modulus of hard and brittle semiconductor wafer materials after microwave radiation. K c It refers to the fracture toughness of hard and brittle semiconductor wafer materials after microwave radiation.

7. The processing method of the microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 3, characterized in that: The processed hard and brittle semiconductor wafers are mounted onto the worktable; Place the microwave irradiation head on one side of the hard and brittle semiconductor wafer to be processed, and determine the relative position of the microwave irradiation head and the surface of the hard and brittle semiconductor wafer. The non-microwave-absorbing grinding fluid is evenly sprayed onto the surface of the hard and brittle semiconductor wafer to be processed through a spraying device. A microwave generator uses microwave radiation to perform "low-temperature" plastic modification on the surface material of a hard and brittle semiconductor wafer to be processed, adjusting the microwave heating position and the size of the microwave irradiation area; The worktable drives the hard and brittle semiconductor wafers to rotate; The grinding wheel processing unit is installed on the Z-axis movable platform of the machine tool, and the Z-axis is moved to perform tool setting and grinding. After processing is complete, turn off the microwave generator and the vacuum self-rotating grinding table, retract the tool to a safe position, and simultaneously return the microwave generator to a safe position.

8. The processing method of the microwave back-subtraction processing system for hard and brittle semiconductor wafers as described in claim 7, characterized in that: Critical cutting depth of hard and brittle semiconductor wafers d c = λ ( H / E ) 1 / 2 ( K c / H) 2 In the formula λ It is the brittle-plastic transition factor for hard and brittle semiconductor wafer materials. H It refers to the hardness of brittle semiconductor wafer materials after microwave radiation. E It is the elastic modulus of hard and brittle semiconductor wafer materials after microwave radiation. K c It refers to the fracture toughness of hard and brittle semiconductor wafer materials after microwave radiation.

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