A combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices

Abstract

The present invention relates to a combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices. The process comprises the following steps: using a coarse-grained grinding wheel for rough grinding to achieve rapid thinning and determine the depth of the subsurface damage layer, providing a reference for the grinding wheel feed rate in the fine grinding stage; using a fine-grained grinding wheel for fine grinding to remove the damage layer introduced in the rough grinding stage, and obtaining higher surface / subsurface quality and surface accuracy by optimizing process parameters; using aluminum oxide (Al2O3) abrasives to prepare a special polishing liquid for photochemical mechanical polishing, and performing semi-fine polishing on the laser crystal slices to quickly remove the surface damage caused in the grinding stage; using zirconium oxide (ZrO2) abrasives to prepare a special polishing liquid for photochemical mechanical polishing, and performing fine polishing on the laser crystal slices to further optimize the surface quality and surface accuracy; and using an ultrasonic cleaner to clean the laser crystal slices, with anhydrous ethanol as the cleaning agent. The present invention can simultaneously achieve high surface integrity and high-efficiency processing of laser crystal slices.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-precision processing of laser crystal slices in thin-slice lasers, and in particular to a combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices. Background Art

[0002] Thin-disk lasers have become the future development direction of high-power lasers due to their extremely thin gain medium, high pumping efficiency, and small wavefront distortion, as well as the compact structure of solid-state lasers. Among them, the gain medium is the core component of the thin-disk laser, and the preparation quality directly affects the performance and service life of the laser. Common gain media (such as YAG, Lu2O3, and GGG laser crystal slices) have the characteristics of high hardness, high brittleness, and strong chemical inertness. At the same time, due to the thin thickness of the laser crystal slice and the large diameter-to-thickness ratio, the warping deformation caused by processing and holding makes it difficult to ensure the surface accuracy requirements.

[0003] Laser crystal slices are mainly processed by a combination of grinding and polishing. However, there are two problems with the combination of traditional grinding and chemical mechanical polishing for laser crystal slices: on the one hand, the material removal rate is low when using free abrasives to grind laser crystal slices, and the large abrasive particles in the grinding fluid can easily cause deep scratches and subsurface damage on the processed surface of the laser crystal slice, thereby increasing the processing time of the subsequent polishing process; on the other hand, due to the stable chemical properties of the material of laser crystal slices, the chemical reaction rate is low when using traditional mechanical polishing, and the mismatch between chemical and mechanical effects leads to low material removal rate and long processing time. In addition, excessive polishing time can lead to poor surface accuracy of laser crystal slices. Summary of the Invention

[0004] In response to the technical problems raised above, a combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices is provided, which includes an ultra-precision grinding stage and a photochemical mechanical polishing stage.

[0005] The ultra-precision grinding stage includes the rough grinding stage and the fine grinding stage. The purpose of the rough grinding stage is to quickly achieve the thinning operation of the laser crystal slice and to increase the grinding allowance reference for the fine grinding stage. The purpose of the fine grinding stage is to remove the crystal subsurface damage caused by the rough grinding and to improve the surface precision PV and surface roughness RMS of the laser crystal slice by optimizing the grinding parameters.

[0006] The photochemical mechanical polishing stage includes a semi-fine polishing stage and a fine polishing stage. In the semi-fine polishing stage, the surface damage of the laser crystal slice caused by the grinding stage is removed with the material removal rate as the main focus and the surface quality as the secondary focus without deteriorating the surface accuracy of the laser crystal slice. In the fine polishing stage, the surface quality of the laser crystal slice is optimized with the surface quality as the main focus and the material removal rate as the secondary focus, and the surface accuracy of the laser crystal slice is trimmed to obtain a laser crystal slice with high precision and high surface integrity.

[0007] The technical means adopted in the present invention are as follows:

[0008] A combined process of laser crystal slice ultra-precision grinding and photochemical mechanical polishing comprises the following steps:

[0009] Step 1, Rough Grinding: Paraffin wax is used to fix the laser crystal wafer to a silicon wafer, which is then attached to the vacuum chuck table of a self-rotating ultra-precision grinding machine. During grinding, the grinding wheel and laser crystal wafer rotate about their respective axes, and the grinding wheel is fed along the axial direction of the machine spindle. Deionized water is used as the coolant. A cup grinding wheel with a preset coarse fixed abrasive grit is used to rough-grind the laser crystal wafer based on preset grinding parameters.

[0010] Among them, the raw materials are laser crystal slices such as yttrium aluminum garnet, lutetium oxide, etc. with a diameter of ≥Φ12mm.

[0011] The self-rotating ultra-precision grinding machine includes a vacuum chuck worktable and a grinding wheel. Paraffin wax is used to fix the laser crystal slice at a certain distance from the center of the silicon wafer. The silicon wafer is then adsorbed on the vacuum chuck worktable, ensuring that the center of the silicon wafer coincides with the center of the worktable.

[0012] A cup grinding wheel with a coarse bonded abrasive grain size is used to coarsely grind the laser crystal slices. Reasonable grinding parameters are determined, the thinning efficiency and surface integrity of the laser crystal slices are controlled in a coordinated manner, and the depth of the subsurface damage layer is determined, providing a reference for the material removal allowance in the next process stage.

[0013] Step 2, fine grinding: A cup grinding wheel with a preset finer fixed abrasive grit is used to fine grind the laser crystal slice. Based on the depth of the subsurface damage layer obtained in the rough grinding stage, the total grinding wheel feed in the fine grinding stage is set to remove the damage layer. The grinding process parameters are optimized to achieve good surface / subsurface quality and surface accuracy of the laser crystal slice.

[0014] Step 3, semi-finishing polishing stage: paraffin wax is used to stick the ground laser crystal slice to the carrier plate, and a counterweight is added to the carrier plate to ensure close contact between the workpiece and the polishing pad on the polishing disk of the chemical mechanical polishing device; a polishing liquid specially prepared for the semi-finishing polishing stage of photochemical mechanical polishing is used with aluminum oxide abrasive to semi-finish polish the laser crystal slice, quickly removing surface damage such as scratches and pits caused by the grinding stage and obtaining a laser crystal slice with a better surface morphology; the chemical mechanical polishing device is an automatic polishing machine; and a UV light source is set at a certain position directly above the polishing pad;

[0015] Step 4, fine polishing stage: using zirconium oxide abrasive with lower hardness to prepare a special polishing liquid for the photochemical mechanical polishing fine polishing stage, and fine polishing the laser crystal slice after semi-fine polishing;

[0016] In step 3 and step 4, ultraviolet light irradiation is performed by an ultraviolet light emitting device.

[0017] Furthermore, after step 4, step 5 is further provided, using anhydrous ethanol as a cleaning agent, and placing the finely polished laser crystal slice in an ultrasonic cleaning apparatus for cleaning.

[0018] Furthermore, in step 1, the abrasive grain size of the cup grinding wheel is #325 or #600.

[0019] Furthermore, in step 2, the abrasive grain size of the cup grinding wheel is #1500 or #3000.

[0020] Furthermore, in step 1 and step 2, the grinding wheel speed range is 1000-3000 rpm, the laser crystal slice self-rotation speed range is 60-240 rpm, and the grinding wheel axial feed speed range is 5-20 um / min.

[0021] Furthermore, the ultraviolet light emitting device is any one of a mercury lamp, a xenon lamp, a deuterium lamp and a bromine tungsten lamp, with a wavelength range of 180 to 1800 nm and an ultraviolet light intensity of 50 to 150 mw / cm 2 .

[0022] Furthermore, in step 3 and step 4, the polishing load is 10-40 kPa, the polishing disc rotation speed is 50-90 rpm, the polishing liquid flow rate is 2-14 ml / min, and the polishing pad is a polyurethane polishing pad IC1000.

[0023] Furthermore, in step 3 and step 4, the abrasive particle size in the special polishing liquid is 20 to 500 nm, and the abrasive concentration is 20 to 110 g / L.

[0024] Furthermore, in step 3 and step 4, in addition to alumina abrasive and zirconia abrasive, the remaining additive components include 0.05-0.20 g / L semiconductor photocatalyst, 5-20 g / L electron capture agent, pH regulator, and 1-5 g / L abrasive dispersant, and the pH regulator adjusts the pH value of the solution to 2-5.

[0025] Furthermore, the semiconductor photocatalyst is at least one of MnFe2O4, CuFe2O4 and CoFe2O4 spinel ferrites; the electron capture agent is at least one of hydrogen peroxide H2O2, peracetic acid CH3COOOH, sodium dichromate Na2Cr2O7 and potassium permanganate KMnO4; the regulator is one of HNO3, H2SO4, H2CO3 and phosphoric acid; the abrasive dispersant is at least one of sodium dodecylbenzene sulfonate SDBS, sodium hexametaphosphate SH, polyvinyl pyrrolidone PVP, sodium polyacrylate SP, polyethylene glycol PEG2000 and sodium tripolyphosphate STPP.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. High processing efficiency: Under the premise of given surface quality and surface accuracy, the total processing time used for the traditional process route (grinding + traditional chemical mechanical polishing) is about 14.5 hours, while the total processing time used for the new combined processing method of the present invention (ultra-precision grinding + photochemical mechanical polishing) is up to about 5 hours, and the processing efficiency is increased by nearly 3 times.

[0028] 2. Good surface / subsurface quality: By using the new combined process method of the present invention to process laser crystal slices, a surface roughness RMS < 0.30 nm and a surface quality without surface / subsurface damage can be obtained.

[0029] 3. High surface accuracy: The combined process method of the present invention can achieve an average surface accuracy PV of 60nm<1 / 10λ@632.8nm for the laser crystal slices obtained, which is much higher than the processing quality of traditional processing technology.

[0030] The invention has reasonable design, low processing cost, strong universality, and is suitable for batch processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1This is a schematic diagram of the processing principles of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices according to the present invention.

[0033] Figure 2 This is the process roadmap for the combined processing of laser crystal slices described in the present invention, wherein (a) is self-rotating ultra-precision grinding; (b) is photochemical mechanical polishing.

[0034] Figure 3 Optical surface diagram of the surface quality and surface accuracy of laser crystal thin slice processing, where (a) is the 3D surface morphology; (b) is the sub-surface morphology; and (c) is the surface accuracy PV.

[0035] Figure 4 These are samples of laser crystal slices processed in batches, where (a) is a YAG laser crystal slice; (b) is a Lu2O3 laser crystal slice.

[0036] Figure 5 The figure compares the processing efficiency of the new combined process method of the present invention with that of the traditional process.

[0037] In the figure: 1. Laser crystal slice; 2. Silicon wafer; 3. Vacuum chuck worktable; 4. Spindle axial direction; 5. Cup grinding wheel; 6. Counterweight; 7. Laser crystal slice; 8. Polishing disk; 9. Ultraviolet light emitting device; 10. Polishing liquid; 11. Loading tray; 12. Polishing pad. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0042] In the description of the present invention, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0043] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0044] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0045] like Figures 1 to 5 As shown, the embodiment of the present invention discloses a combined process of laser crystal slice ultra-precision grinding and photochemical mechanical polishing.

[0046] The self-rotating ultra-precision grinding device includes a vacuum chuck table 3 and a cup grinding wheel 5. In this embodiment, the laser crystal wafer 1 is fixed with paraffin wax 35 mm from the center of the silicon wafer 2, while the silicon wafer 2 is attached to the vacuum chuck table 3, ensuring that the center of the silicon wafer 2 coincides with the center of the table 3. During the grinding process, the cup grinding wheel 5 and the laser crystal wafer 1 rotate about their respective axes, while the cup grinding wheel 5 is fed along the axial direction 4 of the machine tool spindle. Deionized water is used to remove heat and chips generated during the workpiece grinding process.

[0047] During the rough grinding process, a cup-type grinding wheel (5) with a coarse bonded abrasive is used to rough grind the laser crystal slice (1). Optimal grinding parameters are determined to coordinate thinning efficiency and surface integrity. The depth of the subsurface damage layer is determined, providing a reference for the total amount of grinding in the next process stage. This removes the subsurface damage layer caused by rough grinding. This process takes 38 minutes to 2.5 hours.

[0048] During the fine grinding process, a cup grinding wheel 5 with a finer bonded abrasive grit is used. Based on the depth of the subsurface damage layer observed during the rough grinding phase, the total feed rate of the cup grinding wheel 5 is set to remove the damaged layer. Subsequently, by optimizing the grinding process parameters, a laser crystal slice 1 with excellent surface and subsurface quality and high surface accuracy is achieved. This process takes 1 to 10 minutes.

[0049] Semi-finish polishing: The polishing stage utilizes a dedicated photochemical mechanical polishing device, including a UV light emitter 9 and an automatic polisher. UV light source 9 is positioned 15 cm above the polishing pad. Paraffin wax is used to evenly adhere the ground laser crystal slice 7 to the carrier plate. Counterweights 6 are added to carrier plate 11 to ensure close contact between the laser crystal slice 7 and polishing pad 12 on polishing disk 8. A polishing slurry 10, specifically designed for the semi-finish polishing stage of photochemical mechanical polishing, is prepared using aluminum oxide abrasive. Semi-finish polishing is then performed on the laser crystal slice 7, rapidly removing surface defects such as scratches and pits caused by the grinding stage and resulting in a laser crystal slice 7 with a superior surface morphology. This processing time is 40 to 60 minutes.

[0050] Finish polishing: During the final polishing phase of the laser crystal wafer 7, a photochemical mechanical polishing slurry 10 prepared with relatively low-hardness zirconium oxide abrasive is used to polish the semi-finished laser crystal wafer 7, further optimizing the workpiece surface quality and surface accuracy. This process takes 60 to 90 minutes.

[0051] Workpiece Cleaning: After fine polishing, the laser crystal slice 7 is placed in an ultrasonic cleaner for cleaning using anhydrous ethanol to remove residual abrasives, chemicals, and other contaminants from the surface, resulting in a clean surface. This process takes 10 to 30 minutes.

[0052] Example 1

[0053] In this embodiment, the raw material processed is yttrium aluminum garnet with a diameter of 15 mm.

[0054] The laser crystal slice was coarsely ground using a #325 cup grinding wheel. The grinding wheel speed was 2800 rpm, the laser crystal slice self-rotation speed was 150 rpm, the grinding wheel axial feed speed was 15 μm / min, and the processing time was 2 h.

[0055] A #1500 cup grinding wheel was used. The total cup grinding wheel feed rate for the fine grinding phase was set based on the depth of the subsurface damage layer of the laser crystal slice during the rough grinding phase to remove the damaged layer. The grinding wheel speed was 1200 rpm, the laser crystal slice rotation speed was 150 rpm, and the axial feed rate was 15 μm / min. The processing time for this phase was 5 minutes.

[0056] Of course, in the actual processing process, since it is not easy to determine the actual processing allowance, after setting the grinding parameters, adjustments can be made within the set range during the specific processing time period. The same applies to the following embodiments.

[0057] Semi-finishing polishing process stage: set up a mercury lamp light source with a wavelength of 254nm and an ultraviolet light intensity of 50-150mw / cm 2 A polishing slurry specifically designed for the semi-finishing stage of photochemical mechanical polishing (PCMP) was prepared using aluminum oxide abrasive. Semi-finish polishing of laser crystal wafers was performed using an abrasive particle size of 20 to 500 nm at an 80 g / L abrasive concentration. The slurry also contained 0.05 g / L MnFe₂O₄, 15 g / L potassium permanganate (KMnO₄), a pH adjuster (5 g / L sodium dodecylbenzenesulfonate, SDBS), and sodium hexametaphosphate (SH). The pH of the solution was adjusted to 3 using H₂SO₄. This rapidly removed surface defects such as scratches and pits caused by the grinding process, resulting in a laser crystal wafer with a well-defined surface morphology. The polishing load was 40 kPa, the polishing disk speed was 90 rpm, and the polishing slurry flow rate was 10 ml / min. The processing time for this stage was 40 minutes.

[0058] During the fine polishing process, a photochemical mechanical polishing (PCMMP) polishing slurry was prepared using relatively low-hardness zirconium oxide abrasives. The semi-fine polished laser crystal wafers were polished using a slurry with a particle size of 20 to 500 nm and an abrasive concentration of 80 g / L. The slurry also contained 0.05 g / L MnFe2O4, 15 g / L potassium permanganate (KMnO4), a pH adjuster (5 g / L sodium dodecylbenzenesulfonate, SDBS), and sodium hexametaphosphate (SH). The pH of the solution was adjusted to 3 with H2SO4 to further optimize the workpiece surface quality and surface accuracy. The polishing load was 40 kPa, the polishing disk speed was 90 rpm, and the polishing slurry flow rate was 14 ml / min. The processing time for this stage was 90 minutes.

[0059] After fine polishing, the laser crystal slice is placed in an ultrasonic cleaner for cleaning, using anhydrous ethanol as a cleaning agent to remove residual abrasives, chemicals, and other contaminants on the surface, resulting in a clean laser crystal slice surface. This stage of processing takes 20 minutes.

[0060] The total time was 4 hours and 35 minutes.

[0061] Example 2

[0062] In this embodiment, the raw material processed is Φ12mm yttrium aluminum garnet, and the laser crystal slice is coarse-ground using a #600 cup grinding wheel. The grinding wheel speed is 1800rpm, the laser crystal slice self-rotation speed is 240rpm, the grinding wheel axial feed speed is 10um / min, and the processing time is 1h20min.

[0063] A #3000 cup grinding wheel was used. The total cup grinding wheel feed rate for the fine grinding phase was set based on the depth of the subsurface damage layer of the laser crystal slice during the rough grinding phase to remove the damaged layer. The grinding wheel speed was 1500 rpm, the laser crystal slice rotation speed was 240 rpm, and the axial feed rate was 10 μm / min. The processing time for this phase was 2 minutes.

[0064] Semi-fine polishing process stage: set bromine tungsten lamp, wavelength of 254nm, ultraviolet light intensity of 50-150mw / cm 2A polishing slurry specifically designed for the semi-finishing stage of photochemical mechanical polishing (PCMP) was prepared using aluminum oxide abrasive. Semi-finish polishing of laser crystal wafers was performed using a 100g / L abrasive concentration and a 0.15g / L total concentration of a mixture of MnFe2O4, CuFe2O4, and CoFe2O4, along with 5g / L of hydrogen peroxide (H2O2) and a pH adjuster, 5g / L of sodium tripolyphosphate (STPP). The pH of the solution was adjusted to 2 using H2SO4. This slurry rapidly removed surface defects such as scratches and pits caused by the grinding process, resulting in a laser crystal wafer with a well-defined surface morphology. The polishing load was 30kPa, the polishing disk speed was 65rpm, and the polishing slurry flow rate was 14ml / min. The processing time for this stage was 60min.

[0065] During the fine polishing process, a photochemical mechanical polishing (PCMP) polishing slurry was prepared using relatively low-hardness zirconium oxide abrasives. The semi-fine polished laser crystal wafers were polished using a slurry with a particle size of 20 to 500 nm and a concentration of 100 g / L. The slurry also contained 0.15 g / L CoFe₂O₄, 5 g / L hydrogen peroxide (H₂O₂), a pH adjuster, and 5 g / L sodium tripolyphosphate (STPP). The pH of the solution was adjusted to 2 with H₂SO₄ to further optimize the workpiece surface quality and surface accuracy. The polishing load was 30 kPa, the polishing disk speed was 90 rpm, and the polishing slurry flow rate was 14 ml / min. The processing time for this stage was 60 minutes.

[0066] After fine polishing, the laser crystal slice is placed in an ultrasonic cleaner for cleaning, using anhydrous ethanol as a cleaning agent to remove residual abrasives, chemicals, and other contaminants on the surface, resulting in a clean laser crystal slice surface. This stage of processing takes 20 minutes.

[0067] The total time was 3 hours and 42 minutes.

[0068] Example 3

[0069] In this embodiment, the raw material processed is Φ15mm lutetium oxide, and the laser crystal slice is coarse-ground using a #600 cup grinding wheel. The grinding wheel speed is 1000rpm, the laser crystal slice self-rotation speed is 70rpm, the grinding wheel axial feed speed is 15um / min, and the processing time is 2.5h.

[0070] A #3000 cup grinding wheel was used. The total cup grinding wheel feed rate for the fine grinding phase was set based on the depth of the subsurface damage layer of the laser crystal slice during the rough grinding phase to remove the damaged layer. The grinding wheel speed was 1000 rpm, the laser crystal slice's rotational speed was 70 rpm, and the axial feed rate was 15 μm / min. The processing time for this phase was 10 minutes.

[0071] Semi-finishing polishing process stage: set the xenon lamp with a wavelength of 254nm and an ultraviolet light intensity of 50-150mw / cm 2 A polishing slurry specifically designed for the semi-finishing stage of photochemical mechanical polishing (PCMP) was prepared using aluminum oxide abrasive. Semi-finish polishing of laser crystal wafers was performed using an abrasive particle size of 20 to 500 nm at a concentration of 25 g / L. The slurry also contained 0.20 g / L CuFe2O4, 20 g / L sodium dichromate (Na2Cr2O7), and a pH adjuster containing 1 g / L of polyvinylpyrrolidone (PVP), sodium polyacrylate (SP), and polyethylene glycol (PEG2000). The pH of the solution was adjusted to 5 with HNO3. This rapidly removed surface defects such as scratches and pits caused by the grinding process, resulting in a laser crystal wafer with a well-defined surface morphology. The polishing load was 20 kPa, the polishing disk speed was 50 rpm, and the polishing slurry flow rate was 4 ml / min. The processing time for this stage was 60 minutes.

[0072] During the fine polishing process, a photochemical mechanical polishing (PCMMP) polishing slurry was prepared using relatively low-hardness zirconium oxide abrasives. The semi-finished laser crystal wafers were polished using a slurry with a particle size of 20 to 500 nm and a concentration of 25 g / L. The slurry also contained 0.20 g / L CuFe2O4, 20 g / L sodium dichromate (Na2Cr2O7), and a pH adjuster containing 1 g / L of polyvinylpyrrolidone (PVP), sodium polyacrylate (SP), and polyethylene glycol (PEG2000). The pH of the solution was adjusted to 5 with HNO3 to further optimize the workpiece surface quality and surface accuracy. The polishing load was 20 kPa, the polishing disk speed was 50 rpm, and the polishing slurry flow rate was 4 ml / min. The processing time for this stage was 80 minutes.

[0073] After fine polishing, the laser crystal slice is placed in an ultrasonic cleaner for cleaning, using anhydrous ethanol as a cleaning agent to remove residual abrasives, chemicals, and other contaminants on the surface, resulting in a clean laser crystal slice surface. This stage of processing takes 20 minutes.

[0074] The total time was 5 hours and 20 minutes.

[0075] In summary, compared with the traditional grinding and polishing process, the laser crystal slice ultra-precision grinding and photochemical mechanical polishing combined with the laser crystal slice processing of the present invention can improve the processing efficiency by nearly 3 times, taking Example 1 as an example. Figure 5 As shown, other embodiments are even more efficient. At the same time, by using an optical microscope and a plane interferometer to detect the surface of the laser crystal slice, the surface roughness RMS < 0.3nm, the surface / subsurface is damage-free, the surface accuracy PV < 60nm (1 / 10λ@632.8nm) and the thickness is 100um to 200um, as shown in FIG. Figure 3 、 Figure 4 shown.

[0076] The metal oxides (such as lutetium oxide crystals and sapphire crystals) and garnet crystals (such as yttrium aluminum garnet (YAG) and gadolinium gallium garnet) targeted by this invention, particularly YAG, are among the materials with the greatest potential for application in laser crystals. They are distinct from diamond (molecular formula: C, type: atomic crystal) and silicon wafers (molecular formula: Si or SiC, type: atomic crystal or covalent compound). Laser crystals differ significantly from these other materials in terms of physical and chemical properties.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A combined process of laser crystal thin slice ultra-precision grinding and photochemical mechanical polishing, characterized in that: The steps include: Step 1, Rough Grinding: Paraffin wax is used to fix the laser crystal wafer to a silicon wafer, which is then attached to the vacuum chuck table of a self-rotating ultra-precision grinding machine. During grinding, the grinding wheel and laser crystal wafer rotate about their respective axes, and the grinding wheel is fed along the axial direction of the machine spindle. Deionized water is used as the coolant. A cup grinding wheel with a preset coarse fixed abrasive grit is used to rough-grind the laser crystal wafer based on preset grinding parameters. Step 2, fine grinding: A cup grinding wheel with a preset finer fixed abrasive grit is used to fine grind the laser crystal slice. Based on the depth of the subsurface damage layer obtained in the rough grinding stage, the total grinding wheel feed in the fine grinding stage is set to remove the damage layer. The grinding process parameters are optimized to achieve good surface / subsurface quality and surface accuracy of the laser crystal slice. Step 3, semi-finishing polishing stage: paraffin wax is used to stick the ground laser crystal slice to the carrier plate. A counterweight is added to the carrier plate to ensure close contact between the workpiece and the polishing pad on the polishing plate of the chemical mechanical polishing device. A special polishing liquid for the semi-finishing polishing stage of photochemical mechanical polishing is prepared with aluminum oxide abrasive, and the laser crystal slice is semi-finished. Step 4, fine polishing stage: using zirconium oxide abrasive to prepare a special polishing liquid for the photochemical mechanical polishing fine polishing stage, and fine polishing the laser crystal slice after semi-fine polishing; In step 3 and step 4, ultraviolet light irradiation is performed by an ultraviolet light emitting device; In steps 3 and 4, the abrasive particle size in the special polishing liquid is 20 to 500 nm, and the abrasive concentration is 20 to 110 g / L; In steps 3 and 4, in addition to the alumina abrasive and the zirconia abrasive, the remaining additive components include 0.05 to 0.20 g / L of a semiconductor photocatalyst, 5 to 20 g / L of an electron capture agent, a pH adjuster, and 1 to 5 g / L of an abrasive dispersant, wherein the pH adjuster adjusts the solution pH to 2 to 5; The semiconductor photocatalyst is at least one of MnFe2O4, CuFe2O4 and CoFe2O4 spinel ferrites; the electron capture agent is at least one of hydrogen peroxide H2O2, peracetic acid CH3COOOH, sodium dichromate Na2Cr2O7 and potassium permanganate KMnO4; the regulator is one of HNO3, H2SO4, H2CO3 and phosphoric acid; the abrasive dispersant is at least one of sodium dodecylbenzene sulfonate SDBS, sodium hexametaphosphate SH, polyvinyl pyrrolidone PVP, sodium polyacrylate SP, polyethylene glycol PEG2000 and sodium tripolyphosphate STPP.

2. The combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices according to claim 1, characterized in that: After step 4, step 5 is further provided, using anhydrous ethanol as a cleaning agent, and placing the finely polished laser crystal slice in an ultrasonic cleaning apparatus for cleaning.

3. The combined process of laser crystal thin slice ultra-precision grinding and photochemical mechanical polishing according to claim 1, characterized in that: In step 1, the cup grinding wheel abrasive grit size is #325 or #600.

4. The combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices according to claim 1, characterized in that: In step 2, the cup grinding wheel abrasive grit size is #1500 or #3000.

5. The combined process of laser crystal thin slice ultra-precision grinding and photochemical mechanical polishing according to claim 1, characterized in that: In steps 1 and 2, the grinding wheel speed range is 1000 to 3000 rpm, the laser crystal slice self-rotation speed range is 60 to 240 rpm, and the grinding wheel axial feed speed range is 5 to 20 um / min.

6. The combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices according to claim 1, characterized in that: The ultraviolet light emitting device is any one of a mercury lamp, a xenon lamp, a deuterium lamp and a bromine tungsten lamp, with a wavelength range of 180 to 1800 nm and an ultraviolet light intensity of 50 to 150 mw / cm 2 .

7. The combined process of ultra-precision grinding and photochemical mechanical polishing of laser crystal slices according to claim 1, characterized in that: In steps 3 and 4, the polishing load is 10 to 40 kPa, the polishing disk speed is 50 to 90 rpm, and the polishing liquid flow rate is 2 to 14 ml / min.

Images