Grinding and polishing processing method for ultra-precise YIG single crystal

Abstract

The invention discloses a grinding and polishing processing method of an ultra-precise YIG (yttrium iron garnet) single crystal, which is suitable for a planar YIG (yttrium iron garnet) single crystal (circle) prepared by a liquid phase epitaxy method, a molten salt method and a floating zone melting method, and comprises the following steps: grinding the YIG single crystal, and controlling the thickness and the total thickness deviation (TTV) of the crystal; rough polishing is carried out on the YIG single crystal, and subsurface damage of the wafer is eliminated; and finally, carrying out ultra-precision polishing on the YIG crystal to realize surface planarization with sub-nano-scale surface roughness. According to the method, the surface roughness of the yttrium iron garnet single crystal can be controlled below 1nm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of yttrium iron garnet (YIG) and doped yttrium iron garnet single crystal materials, and particularly relates to a process method for preparing high-precision size and super-precision surface by using a master method for grinding and polishing. BACKGROUND

[0002] Garnet crystal is very similar to the shape and color of pomegranate seeds, and is named as "garnet". Garnet is one of the main rock-forming minerals in the crust and upper mantle. The chemical composition of garnet is relatively complex, and different elements form different combinations, such as magnesium aluminum garnet, iron aluminum garnet, manganese aluminum garnet, calcium chromium garnet, calcium aluminum garnet, calcium iron garnet, etc. With the understanding and utilization of the properties of garnet crystal, some artificial garnet single crystals have appeared, such as yttrium iron garnet (YIG), gadolinium gallium garnet (GGG), yttrium aluminum garnet (YAG), and single crystals obtained by doping them.

[0003] Yttrium iron garnet single crystal and doped yttrium iron garnet single crystal are important raw materials for magneto-optical devices and new microwave devices, and can be prepared by liquid phase epitaxy, molten salt method, optical zone melting method and other processes. However, in the field of magneto-optics and microwave, in order to ensure the use performance of the device (such as insertion loss, microwave loss, etc.), the single crystal material needs to be ground to high-precision size and the surface needs to be polished to super-precision state. The commonly used grinding and polishing process includes mechanical grinding and polishing, chemical grinding and polishing, and grinding and polishing combining the two processes. Mechanical grinding and polishing reduces the surface roughness through physical friction, chemical grinding and polishing uses chemical reaction to preferentially dissolve the micro protrusions on the surface in the medium to obtain a smooth surface, and the master method is a commonly used method in mechanical grinding and polishing process.

[0004] Master method is a key technology to realize high-precision profile replication and high-surface customization in polishing process. The core is to use a stable and high-precision master as a reference, and the profile information of the master is transmitted to the surface of the single crystal material through surface contact processing. Even if the equipment develops from the traditional classical multi-axis polishing machine to the full-automatic crystal grinding and polishing machine, the principle does not change. Different application scenarios have different size requirements for YIG single crystal materials, as small as φ2mm and as large as φ76.2mm. Different application scenarios also have different requirements for the shape of YIG single crystal materials, and the commonly used shapes include circular, square, rectangular, hexagonal, etc. Compared with chemical grinding and polishing, mechanical grinding and polishing master method can better meet the ultra-precision machining requirements such as size and shape in different application scenarios. In addition, for different terminal applications, different crystal orientations of YIG crystals are required, usually including high-hardness crystal planes (100), (110) and low-hardness crystal plane (111), etc. Therefore, during the grinding and polishing process, directional cutting is required to obtain the required crystal orientation and reduce the risk of fracture, and then the surface is polished. This also makes the master method process cannot be replaced by the chemical grinding and polishing process.

[0005] At present, there are many reports on the grinding and polishing processing of garnet single crystal materials. Usually, gadolinium gallium garnet (GGG), yttrium aluminum garnet (YAG), Nd-doped yttrium aluminum garnet (Nd:YAG) and other single crystal materials are processed by mechanical grinding and polishing combined with chemical grinding and polishing to obtain a crystal surface with a surface roughness of not higher than 0.5nm (such as CN119304693A). However, it is difficult to control the size and shape of the crystal. Mechanical grinding and polishing can make the crystal obtain the required size and shape, but the surface roughness of the crystal obtained by mechanical grinding and polishing is difficult to control below 1nm.

[0006] There are few reports on the method for processing yttrium iron garnet (YIG) and doped yttrium iron garnet single crystals of different sizes and shapes in the prior art, especially for preparing an ultra-smooth surface with a surface roughness Ra<1.0 nm. Different from most garnet materials which are grown into single crystals by the Czochralski method, YIG single crystals are mainly prepared by fluxed melt method or liquid phase epitaxy method. For YIG single crystals prepared by fluxed melt method, the presence of fluxing agent will cause more defects (such as inclusions) in the crystal, and the size of the crystal is generally small, resulting in high difficulty in grinding and polishing. In the process of preparing YIG crystal by liquid phase epitaxy method, GGG is usually used as a substrate. Due to the deviation of the lattice constant and the thermal expansion coefficient of YIG and its substrate GGG crystal, internal stress is formed between YIG epitaxial film and GGG substrate, which is difficult to completely eliminate by thermal annealing, resulting in warping of YIG wafer and easy breaking during grinding and polishing process, which increases the difficulty of processing. SUMMARY

[0007] Aiming at the current existing technical problems, the application focuses on the super-precision grinding and polishing process of yttrium iron garnet and doped yttrium iron garnet single crystal, and proposes a general mechanical grinding and polishing master method processing technology, which can process YIG single crystal planes of different molecular formulas, different sizes, different shapes and different crystal directions, and finally obtain optical grade size precision and surface precision. This process can freely process YIG single crystals prepared by molten salt method, liquid phase epitaxy method, floating zone melting method and other crystal growth methods and achieve the corresponding indicators required by different application scenarios. Its main features are: it can process YIG single crystals and doped YIG single crystals of different sizes, (100), (110), (111) surfaces obtained by directional cutting, the process is universal, and the polishing time only differs by a few minutes, suitable for YIG material production with different molecular requirements. At the same time, considering the internal stress and warping characteristics of liquid phase epitaxial YIG single crystal and doped YIG single crystal (Bi-doped YIG magneto-optical single crystal or Ga-doped YIG magneto-optical single crystal for optical isolator), the selected abrasive, polishing disc, processing pressure and speed will not damage the epitaxial wafer, and can be processed to the corresponding indicators (including shape, size, thickness, final Ra, etc.).

[0008] The mother version grinding and polishing process provided by the application is aimed at processing YIG single crystal planes of different molecular formulas, different sizes and different shapes, and involves the technical principle of mother version processing principle, that is, using different grinding and polishing powders and grinding and polishing discs to grind the surface of the YIG single crystal, by constantly replacing the combination of grinding and polishing powders and grinding and polishing discs, adopting the four-step processing of "rough grinding-precision grinding-rough polishing-precision polishing", and adjusting the four-stage grinding disc speed and processing pressure, the size and surface of the YIG single crystal are processed. In the process, the accuracy of the processing is mainly controlled by the grinding and polishing system (combination of grinding and polishing powder and grinding and polishing disc), grinding and polishing process (such as processing pressure, grinding and polishing disc speed, etc.).

[0009] To achieve the above object, the technical scheme adopted by the application is:

[0010] A super-precision YIG single crystal grinding and polishing processing method, which adopts rough grinding, precision grinding, rough polishing and precision polishing four-step process in sequence, and each step reaches the following conditions:

[0011] The rough grinding end point is: the processing allowance of the wafer blank is 20-50μm, and the TTV control is less than or equal to 10μm;

[0012] The precision grinding end point is: the processing allowance of the wafer is 1-2μm, and the TTV control is less than or equal to 3μm;

[0013] The rough polishing end point is: under naked eye observation, no pitting, sand inclusion and scratch on the surface of the crystal can be observed;

[0014] The precision polishing end point is: the surface roughness Ra<1nm;

[0015] In the four-step process, the rotation speed of the grinding disc and the mirror disc is less than 50 rpm, the rotation speed of the grinding disc and the mirror disc differs by 0-10 rpm, preferably 4-6 rpm.

[0016] More specifically, the method comprises the following steps:

[0017] Step 1, rough grinding:

[0018] The YIG single crystal wafer is rough ground by the first grinding and polishing machine to obtain a wafer blank, and the end point of the rough grinding is that the rough grinding is performed until the processing allowance of the wafer blank is 20-50 μm, and the total thickness deviation (TTV) is controlled to be less than or equal to 10 μm;

[0019] The grinding and polishing powder used by the first grinding and polishing machine is boron carbide with W20~W40 or diamond;

[0020] The grinding and polishing disc used by the first grinding and polishing machine is a cast iron disc or a tin disc;

[0021] The pressure is 95~105 g / cm 2 ;

[0022] The rotation speed of the grinding disc is 39~41 rpm;

[0023] The rotation speed of the mirror disc is 44~46 rpm;

[0024] The rotation speed of the grinding disc and the mirror disc differs by less than 10 rpm, preferably 4-6 rpm.

[0025] Step 2, fine grinding

[0026] The wafer blank obtained in step 1 is fine ground on the second grinding and polishing machine to obtain a fine ground wafer, and the end point of the fine grinding is that the processing allowance of the fine ground wafer is 1-2 μm, and the total thickness deviation TTV is controlled to be less than or equal to 3 μm;

[0027] The grinding and polishing powder used by the second grinding and polishing machine is boron carbide with W10~W14, white corundum or diamond;

[0028] The grinding and polishing disc used by the second grinding and polishing machine is a cast iron disc or a ceramic disc;

[0029] The pressure is 74~76 g / cm 2 ;

[0030] The rotation speed of the grinding disc is 19~21 rpm;

[0031] The rotation speed of the mirror disc is 24~26 rpm;

[0032] The difference between the grinding disc speed and the mirror disc speed should be less than 10 rpm. Preferably, the difference should be 4-6 rpm.

[0033] Step 3, rough polishing

[0034] The finely ground wafer obtained in step 2 is coarsely polished on a third grinding and polishing machine to obtain a coarsely polished wafer. The polishing time is 60~150min.

[0035] The polishing endpoint is when pits, pinholes, and scratches on the crystal surface are no longer visible to the naked eye.

[0036] The third grinding and polishing machine uses corundum, cerium oxide, or diamond powder with a strength of W2 to W3.5.

[0037] The third grinding and polishing machine uses polyurethane discs or damping cloth discs for grinding and polishing;

[0038] The pressure is 74~76 g / cm 2 ;

[0039] The grinding disc rotates at 29~31 rpm;

[0040] The mirror disk rotates at 34~36 rpm;

[0041] The difference between the grinding disc speed and the mirror disc speed should be less than 10 rpm. Preferably, the difference should be 4-6 rpm.

[0042] The purpose of rough polishing is to eliminate surface damage to the finely ground wafer while achieving a surface roughness of <3nm.

[0043] Step 4, fine polishing

[0044] The rough polished wafer obtained in step 3 is finely polished on the fourth grinding and polishing machine to obtain ultra-precision YIG single crystal. The polishing time is 30~60min.

[0045] The endpoint of fine polishing is: surface roughness Ra < 1nm; surface roughness data is obtained by scanning the wafer surface with a surface roughness meter, and polishing is stopped after the requirement is met;

[0046] The fourth grinding and polishing machine uses corundum, silica gel, or cerium oxide with a W of 0.08 to 0.1.

[0047] The polishing pads used in the fourth grinding and polishing machine are made of velvet cloth, damping cloth, or polyurethane.

[0048] Pressure 49~51g / cm 2 ;

[0049] The grinding disc rotates at 15~30 rpm;

[0050] The mirror disk rotates at 20~35 rpm;

[0051] The difference between the grinding disc speed and the mirror disc speed should be less than 10 rpm. Preferably, the difference should be 4-6 rpm.

[0052] The purpose of fine polishing is to flatten the surface of the coarse polished crystal surface, so that the surface roughness reaches Ra<1nm.

[0053] In steps 1 to 4, the rotation speed of the mirror disk is greater than or equal to the rotation speed of the grinding disk, and the rotation direction is the same.

[0054] Optionally, during the grinding and polishing process, the grinding and polishing disc can be grooved, such as radial grooves or orthogonal grooves, to increase grinding efficiency; preferably, a grooved grinding and polishing disc is used in the rough grinding and rough polishing steps, while an ungrooved grinding and polishing disc is used in the fine grinding and fine polishing steps.

[0055] The raw material for rough grinding in step 1, "YIG single crystal wafer", can be a YIG single crystal wafer grown on a GGG substrate by liquid phase epitaxy, or a YIG single crystal wafer prepared by means of molten salt method, optical floating zone method, etc. Before rough grinding, the YIG single crystal wafer is cut into single crystal wafers (rods) by processing methods such as cutting, and thus used as the raw material for rough grinding.

[0056] In the four-step process of coarse grinding, fine grinding, coarse polishing and fine polishing, the polishing powder is prepared into polishing liquid and used on the corresponding grinding and polishing machine.

[0057] Preferably, step 1 uses any one of the following combinations of process parameters:

[0058] Table 1 Processing Technology Table for Step 1

[0059] Combination No. Abrasive powder Abrasive plate pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) MRR (μm / min) Surface roughness achievable by the process (μm) 1 Bor-on W40 Cast iron 100 40 45 10 1.250±0.112 2 Bor-on W28 Cast iron 100 40 45 6 0.800±0.108 3 Bor-on W20 Cast iron 100 40 45 4 0.650±0.088 4 Diamond W20 Tin 100 40 45 6 0.600±0.076

[0060] Preferably, step 2 uses any one of the following combinations of process parameters:

[0061] Table 2 Processing Technology Table for Step 2

[0062] Combination No. Abrasive powder Abrasive plate pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) MRR (μm / min) Surface roughness achievable by the process (μm) 1 Bor-on W14 Cast iron 75 20 25 3 0.480±0.108 2 Bor-on W10 Cast iron 75 20 25 2 0.420±0.102 3 White corundum W10 Ceramic 75 20 25 1 0.250±0.026 4 Diamond W10 Ceramic 75 20 25 2 0.320±0.038

[0063] Preferably, step 3 uses any one of the following combinations of process parameters:

[0064] Table 3 Processing Technology Table for Step 3

[0065] Combination No. Abrasive powder Abrasive plate pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) Polishing time (min) Surface roughness achievable by the process (nm) 1 Corundum W3.5 Polyurethane 75 30 35 120 ＜3 2 Cerium oxide W3 Polyurethane 75 30 35 120 ＜3 3 Cerium oxide W3 Damp cloth 75 30 35 150 ＜3 4 Diamond W3.5 Polyurethane 75 30 35 60 ＜3 5 Diamond W3.5 Damp cloth 75 30 35 60 ＜3 6 Diamond W2 Polyurethane 75 30 35 90 ＜3

[0066] A surface roughness of less than 3 nm means that pits, pinholes, and scratches on the crystal surface cannot be observed with the naked eye.

[0067] Preferably, step 4 uses any one of the following combinations of process parameters:

[0068] Table 4 Processing Technology Table for Step 4

[0069] Combination No. Abrasive powder Abrasive plate pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) Polishing time (min) Surface roughness achievable by the process (nm) 1 Corundum W0.1 Velvet cloth 50 15 20 60 ＜1 2 Silicone W0.08 Velvet cloth 50 30 35 60 ＜1 3 Silicone W0.08 Velvet cloth 50 15 23 60 ＜1 4 Silicone W0.08 Damp cloth 50 15 20 30 ＜1 5 Cerium oxide W0.1 Velvet cloth 50 15 20 60 ＜1 6 Cerium oxide W0.1 Polyurethane 50 30 35 60 ＜1

[0070] Furthermore, in the actual process, steps 1 to 4 can be freely combined in the process combinations shown in Tables 1 to 4, but it is necessary to ensure that the machining allowance and total thickness meet the requirements at the end of each step, and that the crystal surface roughness meets the requirements in the table, so that the final surface roughness can reach below 1 nm.

[0071] During the grinding process, the rotational speed difference between the mirror disc (fixed on the fixture) and the grinding disc, driven by the motor, is 0-10 rpm. This is primarily to ensure kinetic stability during grinding: ensuring stable equipment operation and stable removal of material from the crystal surface, and minimizing the total volume transition time (TTV). A preferred difference of 5 rpm between the mirror disc and the grinding disc rotational speeds not only guarantees high grinding efficiency but also ensures grinding accuracy. Similarly, during polishing, maintaining the rotational speed difference between the mirror disc and the polishing disc within 0-10 rpm is suitable. The mirror disc rotational speed setting is more flexible during polishing than during grinding; increasing the speed can improve polishing efficiency, but increasing the speed requires increasing the polishing slurry supply to avoid disc skipping and dry grinding.

[0072] Whether in the grinding or polishing stage, when processing YIG crystals on a jig-type single-sided grinding and polishing machine, it is recommended to keep the speed difference between the mirror disk and the grinding disk within 0-10 rpm.

[0073] Furthermore, a grinding and polishing method for ultra-precision YIG single crystals employs the following process conditions:

[0074] Step 1 uses combination number 2 from Table 1;

[0075] Step 2 uses combination number 2 from Table 2;

[0076] Step 3 uses combination number 4 from Table 3;

[0077] Step 4 uses combination number 4 from Table 4;

[0078] That is, the process conditions shown in Table 5 are adopted:

[0079] Table 5 Optimal Process Conditions for Grinding and Polishing of Ultra-Precision YIG Single Crystals

[0080] Step Abrasive powder Abrasive plate pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) Polishing time (min) 1 Bor-on W28 Cast iron 100 40 45 / 2 Bor-on W10 Cast iron 75 20 25 / 3 Diamond W3.5 Polyurethane 75 30 35 60 4 Silicone W0.08 Damp cloth 50 15 20 30

[0081] This process condition achieves the lowest Ra among many process conditions, and has wide applicability. It also has a short polishing time, resulting in high processing efficiency.

[0082] The term "grinding and polishing machine" in this invention refers to a collective term for machines with grinding and / or polishing functions, including a first grinding and polishing machine, a second grinding and polishing machine, a third grinding and polishing machine, and a fourth grinding and polishing machine. These machines use different grinding and polishing powders (and grinding and polishing liquids prepared from the powders), different grinding and polishing discs, and differ in pressure, disc rotation speed, and mirror disc rotation speed during use. CMP equipment is a typical core piece of equipment in semiconductor manufacturing for achieving nanoscale planarization of wafer surfaces. CMP equipment can achieve the process conditions for each step of this invention. By combining CMP equipment with the processes of this invention, ultra-precision YIG single crystals can be obtained. CMP equipment can be used as one of the grinding and polishing machines that can be selected for use in this invention, and all four grinding and polishing machines can utilize CMP equipment. Although this invention refers to the grinding and polishing machines as a first grinding and polishing machine, a second grinding and polishing machine, a third grinding and polishing machine, and a fourth grinding and polishing machine, they may be the same grinding and polishing machine, used in different process stages, and differ in process conditions and components.

[0083] The ultra-precision grinding and polishing method for YIG single crystals is suitable for preparing YIG wafers with a thickness accuracy of ±3μm, TTV < 5μm, and surface roughness Ra < 1nm. Before grinding and polishing, the wafer size can be between φ5mm-φ77mm (circular) or between 5×5mm – 11×11mm (square). After grinding and polishing, the wafer thickness can be between 200-4000μm. This process ensures that YIG epitaxial wafers prepared by liquid phase epitaxy (with a YIG / GGG / YIG three-layer crystal structure and significant warpage) do not break during processing. Furthermore, it can be used to prepare three-layer (YIG / GGG / YIG), two-layer (YIG / GGG), or self-supporting single-layer YIG single crystals as needed.

[0084] Terminology Explanation

[0085] "Polishing powder": a general term for grinding powder used in the grinding process and polishing powder used in the polishing process.

[0086] "Polishing disc": A general term for the grinding disc used in the grinding process and the polishing disc used in the polishing process, as well as the polishing pad installed on the grinding disc.

[0087] A "grinding disc" is a rotating platform used in grinding processes and a platform used to mount polishing pads in polishing processes. The grinding disc rotates during the grinding / polishing process.

[0088] The "mirror plate" is fixed to the fixture by vacuum adsorption. The mirror plate is used to fix the wafer and drive it to rotate.

[0089] "Machining allowance" refers to the thickness of the crystal layer that needs to be removed from the surface of the wafer during subsequent processing, through grinding and polishing. Its purpose is to ensure that the final crystal meets the design requirements for dimensional accuracy and surface roughness. Insufficient machining allowance will result in the product thickness or surface roughness failing to meet design standards.

[0090] "Total Thickness Deviation (TTV)" refers to the absolute difference between the maximum and minimum thickness on the same wafer surface.

[0091] "Rough grinding" and "fine grinding" are both grinding processes. They are distinguished by different process conditions and the resulting wafer surface quality. Fine grinding produces wafers with better surface quality than rough grinding, such as a flatter surface and lower surface roughness.

[0092] "Rough polishing" and "fine polishing" are both polishing processes. They are distinguished by different process conditions and the resulting wafer surface quality. Fine polishing produces wafers with better surface quality than rough polishing, with a surface roughness of less than 1 nm.

[0093] Material Removal Rate (MRR) refers to the volume of material removed per unit time, reflecting the efficiency of the processing. An excessively high MRR can easily lead to the crystal failing to meet design dimensions after grinding and polishing.

[0094] "Surface roughness Ra" is a core parameter for evaluating the micro-unevenness of machined surfaces. It is defined as the arithmetic mean of the absolute values ​​of the profile deviations. Ra is calculated by moving a stylus-type profilometer along the surface, recording the profile curve, and calculating the mean of the absolute values ​​of the deviations at all points.

[0095] "Epitaxial film" refers to a single-crystal thin film prepared by liquid phase epitaxy.

[0096] "Thickness accuracy" refers to the difference between the designed thickness and the actual thickness of the crystal after grinding and polishing. The thickness accuracy is highest when the difference is 0.

[0097] In this invention, the range is expressed as X±Y, where X and Y are numbers. X±Y refers to the range of "the difference between X and Y to the sum of X and Y". For example, 1.250±0.112 represents the range of 1.138 to 1.362.

[0098] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0099] The grinding and polishing method of the present invention is applicable to the planar processing of YIG single crystal materials with various molecular structures, sizes and shapes. It can be carried out on different master plate mechanical polishing equipment according to actual application requirements. The grinding and polishing powder and grinding and polishing disc used have a high degree of selectivity, simple operation, strong controllability, and can prepare YIG single crystals with high precision dimensions and ultra-precision surfaces. Attached Figure Description

[0100] Figure 1 This is a flowchart of the master plate grinding and polishing process involved in this invention. (The reference numerals are:)

[0101] 1. Support mold; 2. Polishing disc; 3. Wafer fixture; 4. Upper pressure head; 5. Polishing fluid; 6. Dressing device; 7. Wafer.

[0102] Figure 2 The following are the process flow, technology, and test diagrams for preparing a single-sided polished 3-inch YIG wafer in Example 1: (a) is a photograph of the YIG epitaxial film thickness measured under a metallographic microscope; (b) is a photograph of the 3-inch YIG single crystal being attached to a mirror disk; (c) is a photograph of the mirror disk carrying the wafer being vacuum-adsorbed onto a fixture; (d) is a photograph of the grinding and polishing machine during the fine grinding process; and (e) is an AFM test diagram of the final polished surface.

[0103] Figure 3 The images shown in Table 7 are atomic force microscopy (AFM) images of the final processed surfaces of some (doped) YIG wafers. (a) corresponds to sample 1 in Table 7, (b) corresponds to sample 4 in Table 7, (c) corresponds to sample 6 in Table 7, and (d) corresponds to sample 10 in Table 7. Detailed Implementation

[0104] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0105] Grinding and polishing process flow:

[0106] like Figure 1As shown, the master-plate method single-sided grinding and polishing equipment has a support mold 1, a grinding and polishing disk 2 mounted on the support mold 1, and a wafer clamp 3 above the grinding and polishing disk. The mirror disk is vacuum-adsorbed onto the clamp, and the wafer 7 is mounted on the disk using a pseudo-photoresist method. An upper pressure head 4 is located above the wafer clamp for pressure adjustment. The clamp drives the mirror disk to rotate, and the wafer on the mirror disk rotates accordingly. The support mold drives the grinding and polishing disk to rotate, and a grinding and polishing liquid 5 made of grinding and polishing powder is added to the grinding and polishing disk. In addition, the master-plate method single-sided grinding and polishing equipment also has a dressing device 6 to trim the grinding and polishing disk. The clamp allows the wafer to contact the grinding and polishing disk and rotate, generating friction to perform grinding and polishing.

[0107] This invention utilizes a master-plate method single-sided grinding and polishing equipment to perform a four-step grinding and polishing process. After the crystal blank is mounted on a plate, it is sequentially subjected to coarse grinding by a first grinding and polishing machine, fine grinding by a second grinding and polishing machine, coarse polishing by a third grinding and polishing machine, and fine polishing by a fourth grinding and polishing machine. Different grinding and polishing powders are used to prepare grinding and polishing solutions during the grinding and polishing process, and different pressures are applied to the wafer during the grinding and polishing process. The rotation speed of the mirror plate and the grinding plate are adjusted to control the speed difference.

[0108] Example 1:

[0109] A method for grinding and polishing ultra-precision YIG single crystals, comprising the following steps:

[0110] Step 1: Using a 3-inch liquid-phase epitaxial Ga-doped YIG single-crystal thin film as the substrate, the epitaxial film thickness is 160 μm (excluding the substrate). The mirror disk is mounted using a pseudo-photoresist method, and the mirror disk is vacuum-adsorbed onto the fixture. On a fixture-type single-sided first-sided grinding and polishing machine, W28 boron carbide polishing slurry (prepared from boron carbide and water, with a solid content of 15-20%) is added via a peristaltic pump at a rate of 20 cc / min. Rough grinding is performed on the cast iron grinding disc, with pressure increased to 100 g / cm³. 2 The grinding disc rotation speed was set to 40 rpm, the mirror disc rotation speed to 45 rpm, the total fixture diameter to φ120 mm, the mirror disc diameter to φ80 mm, the grinding disc width to 100 mm, and the grinding disc with radial grooves (groove spacing 15 mm). The fixture oscillation amplitude was 6°, and the oscillation rate was 10 tpm. The machining allowance Δ1 = 50 μm, and the material removal rate MRR = 6 μm / min. After machining, the total thickness of the rough-ground surface was approximately TTV = 9 μm, and the surface roughness was 0.862 μm. The machining allowance was approximately 20 μm.

[0111] Step 2: Remove the mirror disc and clean it to prevent cross-contamination of abrasive particles. Attach the mirror disc to the fixture and, using a fixture-type single-sided secondary grinding and polishing machine, apply W10 boron carbide polishing slurry (a mixture of boron carbide and water, with a solid content of 10-15%) via a peristaltic pump at a rate of 20 cc / min. Perform fine grinding on the cast iron grinding disc. Apply pressure to 75 g / cm³. 2The grinding disc is set to a rotation speed of 20 rpm, the mirror disc to 25 rpm, the fixture has a total diameter of φ120 mm, the mirror disc diameter of φ80 mm, and the grinding disc width of 100 mm. The grinding disc is ungrooved. The fixture oscillation amplitude is 6°, and the oscillation rate is 5 tpm. The machining allowance Δ2 = 20 μm, and the MRR = 2 μm / min. After machining, the surface finish is TTV = 3 μm, and the surface roughness is 0.408 μm. The machining allowance is approximately 1 μm.

[0112] Step 3: Remove the mirror disk and clean it to prevent cross-contamination of abrasive particles. Attach the mirror disk to the fixture and use a fixture-type single-sided third-sided grinding and polishing machine. Apply W3.5 diamond polishing powder (prepared from diamond polishing powder and water-based diamond dispersion, 3% solids content) via a peristaltic pump at a rate of 4 cc / min. Perform a rough polishing process on an LP-66 red polyurethane polishing pad. Pressurize to 75 g / cm³. 2 The polishing pad rotates at 30 rpm, the mirror disk rotates at 35 rpm, the total diameter of the fixture is φ120 mm, the diameter of the mirror disk is φ80 mm, the diameter of the polishing disk is φ420 mm, the polishing pad has orthogonal grooves (side length 20 mm, groove width 2 mm), the fixture swing amplitude is 15°, and the swing rate is 20 tpm. The rough polishing time is 60 minutes. Scratches and pinholes are not visible to the naked eye on the wafer surface under LED light reflection.

[0113] Step 4: Remove the mirror disk and clean it to prevent cross-contamination of the abrasive particles. Place the mirror disk on the magnetic separator, which has an outer diameter of φ120mm and an inner diameter of φ100mm. Apply pressure to 50 g / cm³ using weights. 2 Polishing was performed on a damping cloth using a clamp-type single-sided fourth-sided grinding and polishing machine with 80-110nm silicone polishing slurry (a commercially available product, diluted with the matching diluent to an abrasive content of 10%-15%). The polishing pad rotation speed was 15 rpm, the mirror disk rotation speed was 20 rpm, and the polishing time was 30 minutes. After polishing, the surface was cleaned and samples were sent for AFM testing. The surface roughness was 0.6836 nm. Thickness testing was performed, and the YIG thickness was approximately 90 μm.

[0114] This embodiment demonstrates that the process can process 3-inch YIG or magneto-optical Ga-doped YIG epitaxial films, control the thickness of the epitaxial film, and polish the surface to optical grade. It can be applied in the processing and production of microwave YIG single crystal materials and magneto-optical YIG single crystal materials.

[0115] Table 6 Key process parameters of Example 1

[0116] Step Abrasive powder Abrasive plate pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) MRR (μm / min) Machining amount (μm) Time (min) Ra 1 Bor-on W28 Cast iron 100 40 45 6 50 8 0.862 μm 2 Bor-on W10 Cast iron 75 20 25 2 20 10 0.408 μm 3 Diamond W3.5 Polyurethane 75 30 35 / / 60 Scratch and pit not observed 4 Silicone W0.08 Damp cloth 50 15 20 / / 30 0.6836 nm

[0117] Note: / indicates no data.

[0118] Figure 2(a) is a photograph of the YIG epitaxial film thickness measured under a metallographic microscope; (b) is a photograph of a 3-inch YIG single crystal bonded to a mirror disk; (c) is a photograph of the mirror disk being vacuum-adsorbed onto a fixture; (d) is a photograph of the grinding and polishing machine during the fine grinding process; and (e) is an AFM test image of the final polished surface, with Ra of 0.6836 nm.

[0119] Example 2

[0120] The YIG crystals with different molecular formulas, crystal orientations, and sizes were processed using the process conditions shown in Table 5, and the processing results shown in Table 7 were obtained. Other process procedures are referred to in Example 1.

[0121] Table 7 Processing results for different YIG crystals

[0122] No. Molecular formula Crystal orientation Shape Size (mm) Thickness (mm) Preparation method Final Ra (nm) 1 [Y3Fe5O 12 ]]> (111) Circular φ 76.2 0.901 (including substrate) Liquid phase epitaxy 0.1901 2 [Y3Fe5O 12 ]]> (111) Square 10×10 1.000 Molten salt 0.7794 3 [Y3Fe5O 12 ]]> (111) Circular φ 5 4.002 Optical zone melting 0.3539 4 [Y3Fe5O 12 ]]> (110) Square 10×10 0.500 Molten salt 0.2711 5 [Y3Fe5O 12 ]]> (100) Circular φ 25.4 0.820 (including substrate) Liquid phase epitaxy 0.4236 6 Bi 0.16 Ca 0.4 V 0.2 Fe 4.8 O 12 ]]> Not oriented Square 10×10 0.501 Molten salt 0.3431 7 La 0.15 Y 2.85 Fe 4.46 Ga 0.54 O 12 ]]> (110) Circular φ 10 1.001 Molten salt 0.8745 8 La 0.1 Y 2.9 Fe 4.82 Ga 0.18 O 12 ]]> (111) Circular φ 76.2 0.782 (including substrate) Liquid phase epitaxy 0.9621 9 La 0.1 Y 2.9 Fe 4.82 Ga 0.18 O 12 ]]> (100) Circular φ 76.2 0.621 (including substrate) Liquid phase epitaxy 0.5521 10 Tb 1.9 Bi 0.75 Nd 0.25 Fe5O 12 ]]> (111) Circular φ 76.2 1.902 (including substrate) Liquid phase epitaxy 0.3539

[0123] Figure 3 The figures in Table 7 show the atomic force microscopy (AFM) images of the final processed surfaces of some (doped) YIG wafers. (a) shows the 3D morphology and microstructure details of sample 1 in Table 7; (b) shows the 3D morphology and microstructure details of sample 4 in Table 7; (c) shows the 3D morphology and microstructure details of sample 6 in Table 7; and (d) shows the 3D morphology and microstructure details of sample 10 in Table 7. The figures show the final Ra values ​​of samples 1, 2, 6, and 10, all below 0.5 nm, demonstrating that this process has the ability to obtain high-precision surfaces from YIG single crystals with different crystal orientations, growth methods, and doping levels.

[0124] YIG crystals prepared by the molten salt method have a size of 10×10 (square) or φ10 (circular), in cm. The size is relatively small, and this process can be used to grind and polish them to obtain a surface with Ra < 1 nm.

[0125] YIG crystals prepared by liquid phase epitaxy showed no breakage during the grinding and polishing process. In the table above, numbers 1, 5, 8, 9, and 10 all represent YIG crystals prepared by liquid phase epitaxy that underwent grinding and polishing without any breakage.

[0126] Grinding and polishing processes were achieved on high-hardness crystal planes (100), (110) and low-hardness crystal plane (111).

[0127] Example 3

[0128] The YIG crystals prepared by liquid phase epitaxy were polished using the process conditions shown in Table 8. Ra is shown in Table 8. Other process procedures are as described in Example 1.

[0129] Table 8. Processing conditions and Ra of YIG crystal in Example 3

[0130] Step Abrasive powder Abrasive plate Pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) MRR (μm / min) Time (min) Ra 1 Bor-on W40 Cast iron 100 40 45 10 / 1.261 μm 2 Bor-on W14 Cast iron 75 20 25 3 / 0.428 μm 3 Corundum W3.5 Polyurethane 75 30 35 / 120 3 nm 4 Corundum W0.1 Velvet cloth 50 15 20 / 60 0.5 nm

[0131] Example 4

[0132] The YIG crystals prepared by liquid phase epitaxy were polished using the process conditions shown in Table 9. Ra is shown in Table 9. Other process procedures are as described in Example 1.

[0133] Table 9. Processing conditions and Ra of YIG crystal in Example 4

[0134] Step Abrasive powder Abrasive plate Pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) MRR (μm / min) Time (min) Ra 1 Bor-on W20 Cast iron 100 40 45 4 / 0.614 μm 2 White corundum W10 Ceramic 75 20 25 1 / 0.250 μm 3 Diamond W3.5 Damp cloth 75 30 35 / 60 1.0 nm 4 Cerium oxide W0.1 Polyurethane 50 30 35 / 60 0.7 nm

[0135] Example 5

[0136] The YIG crystals prepared by liquid phase epitaxy were polished using the process conditions shown in Table 10. Ra is shown in Table 10. Other process procedures are as described in Example 1.

[0137] Table 10 Processing conditions and Ra of YIG crystal in Example 5

[0138] Step Abrasive powder Abrasive plate Pressure (g / cm 2 ) Rotational speed of abrasive plate (rpm) Rotational speed of mirror plate (rpm) MRR (pm / min) Time (min) Ra 1 Diamond W20 Tin 100 40 45 6 / 0.618 pm 2 White corundum W10 Ceramic 75 20 25 1 / 0.231 pm 3 Diamond W2 Polyurethane 75 30 35 / 90 1.0 nm 4 Silica gel W0.08 Silk cloth 50 30 35 / 60 0.5 nm

[0139] The difference in rotational speed has a significant impact on the process results. Table 11 shows the actual processing results obtained by using different differences in the rotational speeds of the mirror disc and grinding disc in the fine grinding process. Except for the difference in rotational speed, the process used was the same: cast iron grinding disc, W10 alumina grinding powder, and processing pressure of 75 g / cm³. 2 Other conditions are as described in Example 1.

[0140] Table 11. Influence of the ratio of mirror disk and grinding disk rotation speeds on machining in the fine grinding process.

[0141] No. Mirror disc rotation speed rpm Grinding disc rotation speed rpm Rotation speed difference rpm MRR pm / min TTV pm Jump disc frequency times / min 1 20 20 0 0.9±0.2 2.3±0.6 0 2 25 20 5 1.1±0.3 2.1±0.7 0 3 30 20 10 1.2±0.2 3.6±1.4 0 4 35 20 15 1.2±0.3 5.1±2.2 ＜1 5 35 30 5 1.6±0.5 4.7±3.1 1-4 6 45 30 15 1.5±0.7 3.2±2.4 1-4 7 55 30 25 1.8±0.8 5.1±4.2 2-5 8 20 40 20 1.7±1.1 7.1±5.1 ＞10 9 40 40 0 2.1±0.8 4.5±3.8 ＞10 10 60 40 20 2.2±0.6 8.9±2.9 ＞10

[0142] The results in Table 11 show that when the grinding disc speed is 20 rpm and the speed difference is within 5 rpm, the stability of YIG crystal processing is high, and the TTV (Total Velocity) of fine grinding can be controlled at around 3 μm. When the speed difference increases to 10 rpm, the TTV increases. When the speed difference increases to 15 rpm, disc skipping occurs, which leads to uneven grinding / polishing pressure, causing local over-grinding or under-grinding on the workpiece surface, affecting the TTV, grinding surface quality, and causing crystal edge breakage. When the grinding disc speed increases (as shown in Table 5, numbers 5-10), due to the small particle size of the grinding powder, disc skipping will occur regardless of how the disc speed is controlled, seriously affecting the TTV, grinding surface quality, and causing crystal edge breakage. When the grinding disc speed is between 20-30 rpm, increasing the polishing slurry concentration or supply rate can only improve the number of disc skipping events to a limited extent, but cannot completely eliminate disc skipping, and the TTV is high, making it difficult to control at around 3 μm. When the grinding disc speed is >30 rpm, disc skipping occurs more frequently during grinding and polishing, which can easily damage the crystal and cause processing failure. Similar problems can occur when the rotational speed of the mirror disc and grinding disc differs during rough grinding, rough polishing, and fine polishing. Controlling the speed difference to within 10 rpm can effectively reduce the frequency of these problems.

[0143] Although the invention has been described herein with reference to illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope and spirit of the principles disclosed herein. More specifically, various variations and modifications can be made to the components and / or layout of the subject matter combination within the scope of this disclosure. Besides variations and modifications to the components and / or layout, other uses will be apparent to those skilled in the art.

Claims

1. A method for grinding and polishing ultra-precision YIG single crystals, characterized in that, The process involves four steps: coarse grinding, fine grinding, coarse polishing, and fine polishing. The rough grinding endpoint is: the machining allowance of the wafer blank is 20-50μm, and the TTV is controlled to be less than or equal to 10μm; The endpoint of fine grinding is: the machining allowance of the finely ground wafer is 1-2μm, and the TTV is controlled to be less than or equal to 3μm; The endpoint of rough polishing is when pits, pinholes, and scratches on the crystal surface are not visible to the naked eye. The endpoint of fine polishing is: surface roughness Ra < 1 nm; In the four-step process, the rotation speed of the grinding disc and the mirror disc are both less than 50 rpm, and the difference between the rotation speed of the grinding disc and the mirror disc is 0-10 rpm.

2. The grinding and polishing method for ultra-precision YIG single crystals according to claim 1, characterized in that, In the four-step process, the difference between the grinding disc speed and the mirror disc speed is 4-6 rpm.

3. The grinding and polishing method for ultra-precision YIG single crystals according to claim 2, characterized in that, The coarse grinding includes: YIG single crystal wafers are rough-ground to obtain wafer blanks; The polishing powder used is boron carbide or diamond with a W20~W40 rating; The polishing disc used is a cast iron disc or a tin disc; Pressure is 95~105 g / cm 2 ; The grinding disc rotates at 39~41 rpm; The mirror disk rotates at 44~46 rpm.

4. The grinding and polishing method for ultra-precision YIG single crystals according to claim 3, characterized in that, The fine grinding includes: The wafer blank obtained in step 1 is subjected to fine grinding to obtain a finely ground wafer; The polishing powder used is boron carbide, white corundum, or diamond with a strength of W10~W14. The polishing discs used are cast iron discs or ceramic discs; The pressure is 74~76 g / cm 2 ; The grinding disc rotates at 19~21 rpm; The mirror disk rotates at 24~26 rpm.

5. The grinding and polishing method for ultra-precision YIG single crystals according to claim 4, characterized in that, The rough polishing includes: The finely ground wafer obtained in step 2 is subjected to rough polishing to obtain a rough polished wafer. The polishing time is 60~150min. The polishing powder used is corundum, cerium oxide, or diamond with a strength of W2 to W3.5; The polishing disc used is made of polyurethane or damping cloth; The pressure is 74~76 g / cm 2 ; The grinding disc rotates at 29~31 rpm; The mirror disk rotates at 34~36 rpm.

6. The grinding and polishing method for ultra-precision YIG single crystals according to claim 5, characterized in that, The fine polishing includes: The rough polished wafer obtained in step 3 is then finely polished to obtain an ultra-precision YIG single crystal. The polishing time is 30~60 minutes. The polishing powder used is corundum, silica gel, or cerium oxide with a W of 0.08 to 0.

1. The polishing pads used in the polishing discs are made of velvet cloth, damping cloth, or polyurethane. Pressure 49~51g / cm 2 ; The grinding disc rotates at 15~30 rpm; The mirror disk rotates at 20~35 rpm.

7. The grinding and polishing method for ultra-precision YIG single crystals according to claim 1, characterized in that, The following process conditions are adopted: Step 1, coarse grinding: Use W28 boron carbide polishing powder, cast iron polishing disc, and a pressure of 100 g / cm. 2 The grinding disc rotates at 40 rpm, and the mirror disc rotates at 45 rpm. Step 2, Fine Grinding: Use W10 diamond polishing powder, a ceramic polishing disc, and a pressure of 75g / cm. 2 The grinding disc rotates at 20 rpm, and the mirror disc rotates at 25 rpm. Step 3, coarse polishing: Use W3.5 diamond polishing powder, a polyurethane polishing disc, and a pressure of 75 g / cm. 2 The grinding wheel speed is 30 rpm, the mirror wheel speed is 35 rpm, and the polishing time is 60 min. Step 4, Fine Polishing: Use W0.08 silicone polishing powder and a polyurethane polishing disc, with a pressure of 50g / cm. 2 The grinding wheel speed was 15 rpm, the mirror wheel speed was 20 rpm, and the polishing time was 30 min.

8. The grinding and polishing method for ultra-precision YIG single crystals according to any one of claims 1 to 7, characterized in that, When the wafer is round before grinding and polishing, its size is between φ5mm and φ77mm. When the wafer is square before grinding and polishing, its size is between 5×5mm and 11×11mm.

9. The grinding and polishing method for ultra-precision YIG single crystals according to claim 7, characterized in that, The molecular formula of the YIG single crystal is Y3Fe5O. 12 Bi 0.16 Ca 0.4 V 0.2 Fe 4.8 O 12 La 0.15 Y 2.85 Fe 4.46 Ga 0.54 O 12 La 0.1 Y 2.9 Fe 4.82 Ga 0.18 O 12 Any one of them.

10. The grinding and polishing method for ultra-precision YIG single crystals according to claim 9, characterized in that, The crystal orientations of the YIG single crystal include (100), (110), (111) and non-orientation.

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