CN115446671A - Preparation method of sapphire spherical crystal - Google Patents
Preparation method of sapphire spherical crystal Download PDFInfo
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- CN115446671A CN115446671A CN202211401543.5A CN202211401543A CN115446671A CN 115446671 A CN115446671 A CN 115446671A CN 202211401543 A CN202211401543 A CN 202211401543A CN 115446671 A CN115446671 A CN 115446671A
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B1/00—Processes of grinding or polishing; Use of auxiliary equipment in connection with such processes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B29/00—Machines or devices for polishing surfaces on work by means of tools made of soft or flexible material with or without the application of solid or liquid polishing agents
- B24B29/02—Machines or devices for polishing surfaces on work by means of tools made of soft or flexible material with or without the application of solid or liquid polishing agents designed for particular workpieces
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
- B24B49/006—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation taking regard of the speed
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B27/00—Single-crystal growth under a protective fluid
- C30B27/02—Single-crystal growth under a protective fluid by pulling from a melt
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
- C30B29/20—Aluminium oxides
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
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- Crystals, And After-Treatments Of Crystals (AREA)
Abstract
The invention belongs to the technical field of sapphire spherical crystals, and particularly relates to a preparation method of a sapphire spherical crystal, which comprises a sapphire crystal growth step and a sapphire crystal polishing and forming step, wherein the seeding and growth process comprises the following steps: putting the seed crystal downwards, touching the seed crystal with the liquid surface at a speed of 1.5-3mm/min, observing the weight change of the seed crystal after touching the liquid surface, starting to grow the crystal by adjusting the power of growth or melting and adjusting the rushing amount of argon introduced above to be 2-20L/min until the weight of the seed crystal is kept stable, starting to reduce the power after stabilizing for 1-3h, starting to grow the crystal, cooling after the crystal growth process is finished, and crystallizingDislocation density of bulk is less than or equal to 1100ps/cm 2 Single crystallinity is less than or equal to 14 arcsec; the polishing and forming steps of the sapphire crystal comprise: s4, primary spherical surface rough polishing, S5, secondary spherical surface rough polishing, and S6, spherical surface fine polishing. The invention can obviously reduce the processing time, reduce the processing cost and meet the technical indexes of finished products.
Description
Technical Field
The invention belongs to the technical field of sapphire spherical crystals, and particularly relates to a preparation method of a sapphire spherical crystal.
Background
Artificial single crystal sapphire, chemical composition: aluminum oxide, chemical formula: al (Al) 2 O 3 The infrared transmittance is more than or equal to 85 percent, the Mohs hardness is 9 grade, the optical fiber is scratch-resistant, acid-base corrosion-resistant, and has excellent optical performance, physical performance and chemical performance, and the optical fiber is widely applied to the fields of photoelectronics, intelligent wearing, communication, optical equipment and national defense.
The growing method of the sapphire crystal mainly comprises the following steps: a czochralski method (CZ method), a kyo method (KY method), a heat exchange method (HEM method), a film guide method (EFG method), a temperature gradient method (TGT method), and the like. The crystal grown by the kyo method (KY method) has good quality, but has the defects of low production yield, low material utilization rate and the like, the heat exchange method (HEM method) has high automation degree, but has the defects of high cost, high crystal defects and the like, the CZ method has high automation degree and high material utilization rate, but has the defects that the processes of seeding and growth control are not easy to control, the crystal growth is unstable, and the performance of the generated crystal cannot reach the dislocation density, the monocrystallization and the stress-free characteristics of optical-grade sapphire single crystal, so that the crystal is easy to crack in the processing process or the crystal raw material cannot reach the parameter indexes of the crystal material required by optical equipment and the national defense field, particularly the crystal performance cannot meet the requirement of the large-caliber (100-300 mm) sapphire spherical crystal raw material, the large-caliber (100-300 mm) sapphire spherical polishing process is easy to crack and scrap, and the processing cost is greatly increased.
At present, the crystal preparation process for mass production processing of sapphire flat sheets tends to be mature, but the polishing process of sapphire large-caliber spherical surfaces is still continuously carried out by using classical processing processes of other crystals, such as milling, spherical surface rough grinding, spherical surface fine grinding and spherical surface polishing. It should be noted that the sapphire crystal structure exhibits anisotropic characteristics, which determine that the related physical properties also have certain directionality. The hardness of sapphire has different values in different directions, which can be considered as a vector. Research shows that the hardness is represented as an ellipsoid structure in a three-dimensional space, the major axis direction of the ellipsoid is the optical axis direction, the hardness in the optical axis direction is relatively high, the Knoop hardness value is 2000, and the Knoop hardness value perpendicular to the optical axis direction is lower and is 1800, which can explain the phenomenon that sapphire is easily ground into an ellipse in any other places except the optical axis direction in practice. In practical application, as the crystal generates considerable thermal stress in the growth process, the crystal lattice can deform to a certain extent, and the distribution of hardness ellipsoids can also change, generally, the maximum hardness direction of sapphire is not the optical axis direction, but forms a certain angle with the optical axis, generally 60 degrees, specifically refer to the sapphire infrared fairing principle and design of university of vinpoch science university, cast iron grinding tools are adopted for manufacturing large-caliber sapphire spheres, and the grinding powder is boron carbide grinding material, but the phenomena of non-uniformity and the like in the sphere polishing process can be easily caused, and the quality can only be improved by polishing for tens of hours. The difficulty of manufacturing the sapphire spherical crystal is greatly increased, the manufacturing effect is low, the cost is high, the defects that the traditional classical processing technology of other crystals cannot meet the manufacturing requirement of the sapphire spherical crystal are overcome, and solution is needed urgently.
Disclosure of Invention
The invention aims to overcome the defects that the polishing processing period of a large-caliber sapphire spherical surface is long, the processing cost is high and the manufacturing quality of the sapphire spherical surface crystal cannot meet the requirements in the prior art, and provides a preparation method of the sapphire spherical surface crystal, which can reduce the processing time of the spherical surface finish polishing process, reduce the processing cost, ensure that the quality of the sapphire spherical surface crystal meets the requirements, ensure that the surface defect grade B of the sapphire spherical surface crystal is less than or equal to IV grade, the surface shape f-number N is less than or equal to 5, and the local aperture error delta N is less than or equal to 0.5, and meet the technical indexes of finished products.
In order to realize the aim, the invention provides a preparation method of a sapphire spherical crystal, which comprises a sapphire crystal growth step and a sapphire crystal polishing and forming step, wherein the sapphire crystal growth step comprises the steps of loading, assembling a thermal field, heating, melting raw materials and adjustingThe method comprises the following steps of liquid surface temperature adjustment, seeding and growth, wherein the seeding and growth process comprises the following steps: putting the seed crystal downwards, touching the seed crystal with the liquid surface at the speed of 1.5-3mm/min, observing the weight change of the seed crystal through a weighing system after touching the liquid surface, starting to grow the crystal by adjusting the power for growth or melting and adjusting the flushing amount of argon introduced above to be 2-20L/min until the weight of the seed crystal is stable, then starting to reduce the power after stabilizing for 1-3h, starting to grow the crystal, cooling after the crystal growth process is finished, and ensuring that the dislocation density of the obtained sapphire single crystal is less than or equal to 1100ps/cm 2 The single crystallinity according to XRD test is less than or equal to 14 arcsec; and the polishing and forming steps of the sapphire crystal comprise: s1, milling and grinding, S2, roughly grinding the spherical surface, S3, finely grinding the spherical surface, S4, roughly polishing the spherical surface for the first time, S5, roughly polishing the spherical surface for the second time, and S6, finely polishing the spherical surface.
In some preferred embodiments, S2 the spherical rough grinding and S3 the spherical fine grinding each independently satisfy: the Brinell hardness of the adopted grinding tool is 100-270N/mm 2 The heat conductivity coefficient of the grinding tool is less than 45W/(m.K); the grain diameter of the adopted coarse grinding abrasive is 90-110 mu m, and the grain diameter of the adopted fine grinding abrasive is 20-30 mu m.
In some preferred embodiments, the process of spherical rough grinding described in S2 controls the roughness Ra of the obtained sapphire spherical surface to be 1-1.2 μm, and the process of spherical fine grinding described in S3 controls the roughness Ra of the obtained sapphire spherical surface to be 0.25-0.35 μm.
In some preferred embodiments, the spherical primary rough polishing of S4 and the spherical secondary rough polishing of S5 each independently satisfy: the Brinell hardness of the adopted rough polishing grinding tool is 35-50N/mm 2 The heat conductivity coefficient of the rough polishing grinding tool is more than 350W/(m.K), and a polishing solution containing a rough polishing grinding material is adopted, wherein the grain diameter of the rough polishing grinding material is not more than 2.5 mu m, and is preferably less than 1 mu m.
Further preferably, the rough polishing grinding tool comprises a concave spherical grinding tool for rough polishing of the convex surface of the sapphire spherical surface and a convex spherical grinding tool for rough polishing of the concave surface of the sapphire spherical surface, wherein a plurality of circular grooves and a plurality of vertical grooves are formed in the concave spherical surface of the concave spherical grinding tool and the convex spherical surface of the convex spherical grinding tool respectively, the circular grooves are used for distributing polishing solution, and the vertical grooves are used for introducing external air into the space between the rough polishing grinding tool and the sapphire spherical surface; the circular grooves are arranged at intervals in a concentric ring mode by taking the center point of a concave spherical surface grinding tool or a convex spherical surface grinding tool as the center, and the vertical grooves penetrate through the circular grooves and are communicated with the circular grooves and are symmetrically distributed along the center point of the corresponding grinding tool.
More preferably, the groove widths of the circular ring grooves and the vertical grooves are 1-4mm and the groove depths are 1-6mm respectively.
Further preferably, the groove width and the groove depth of the vertical groove are respectively larger than those of the circular ring groove.
More preferably, the sum of the slotted areas of the circular ring groove and the vertical groove in the concave spherical grinding tool is 1/5-3/10 of the area of the concave spherical surface, and the sum of the slotted areas of the circular ring groove and the vertical groove in the convex spherical grinding tool is 1/5-3/10 of the area of the convex spherical surface.
More preferably, the plurality of circular ring slots are arranged at equal intervals, and the plurality of vertical slots are arranged at equal intervals.
In some preferred embodiments, the spherical primary rough polishing in S4 and the spherical secondary rough polishing in S5 are both performed on a grinding machine, the spindle rotation speed and the pendulum axis pendulum speed of the grinding machine in the spherical secondary rough polishing are both controlled to be higher than those of the spherical primary rough polishing, and the pendulum axis pressures of the spherical primary rough polishing in S4 and the spherical secondary rough polishing in S5 are each independently 0.05 to 0.15MPa, preferably 0.1 to 0.15MPa.
More preferably, the process conditions of the first rough polishing of the spherical surface in S4 include: controlling the rotation speed of a main shaft to be 10-30rpm, the swing speed of a swing shaft to be 15-25rpm, and the pressure of the swing shaft to be 0.05-0.15MPa, and/or controlling the surface shape f-number N of the sapphire spherical surface to be less than or equal to 5, and the local error delta N of the aperture to meet the condition that delta N is less than or equal to 1 and is greater than or equal to 0.5.
More preferably, the process conditions of the spherical surface secondary rough polishing in S5 include: the rotating speed of a main shaft is controlled to be 30-50rpm, the swing speed of a swing shaft is controlled to be 20-40rpm, the pressure of the swing shaft is controlled to be 0.05-0.15MPa, and/or the surface defect grade B of the sapphire spherical surface is controlled to be less than or equal to VI grade, the surface shape diaphragm number N is controlled to be less than or equal to 5, and the local error delta N of the diaphragm satisfies that delta N is greater than or equal to 0.5 and less than or equal to 1.
In some preferred embodiments, the spherical fine polishing at S6 satisfies: adopting polishing solution containing fine polishing abrasive with the grain diameter of 500-1000nm.
In some preferred embodiments, the spherical surface finish polishing in S6 is performed on a polishing machine, and the process conditions thereof include: controlling the rotation speed of a main shaft of the polishing machine to be 50-150rpm, the swing speed of a swing shaft to be 20-40rpm, and the pressure of the swing shaft to be 0.05-0.15MPa, and/or controlling the surface defect grade B of the sapphire spherical crystal to be less than or equal to the grade IV, the surface shape diaphragm number N to be less than or equal to 5, and the local error delta N of the diaphragm to be less than or equal to 0.5.
In some preferred embodiments, the preparation method further comprises: before the step of polishing and shaping the sapphire crystal, carrying out first segmentation on the bottom of the ingot obtained in the step of growing the sapphire crystal at a position 200-250mm above the bottom of the ingot to obtain a first upper ingot; and performing second segmentation at the position 130-180mm above the bottom of the first ingot to obtain a second ingot below the first ingot, and taking the second ingot as a raw material for the sapphire crystal polishing and forming step.
Has the beneficial effects that:
the invention controls the seeding and growing processes to make the initial crystal growth more stable, improve the performance of the generated crystal and realize that the dislocation density of the optical-grade sapphire single crystal is less than or equal to 1100ps/cm 2 The single crystallinity is less than or equal to 14 arcseconds, so that the possibility of fragmentation and scrap of a large-caliber (100-300 mm) sapphire spherical surface in the polishing and grinding process of S2-S6 is reduced, the crystal raw material reaches the parameter index of the crystal material required by optical equipment and the national defense field, the yield of finished products is improved, and the production cost is reduced; the polishing and forming steps of the sapphire crystal including two times of rough polishing are matched, so that the polishing and grinding time can be effectively reduced, and the quality of the sapphire spherical crystal is improved. Moreover, the single crystal obtained by the invention has high hardness (for example, up to 2200 daN/mm) and good toughness (for example, up to 2.0mpa.m) 1/2 ) The product has less impurities, can avoid the possibility of influencing the product quality problems such as internal cracking, scratching and the like in the subsequent processing process, can enable the finished product to have higher strength, and can more easily achieve the optical infrared transmittance of more than or equal to 87 percent in the subsequent processing process due to less impurities, so that the finished product is more suitable for the fields of photoelectron, intelligent wearing, communication, optical equipment and national defense.
In the preferred two-time rough polishing scheme of the spherical surface primary rough polishing in S4 and the spherical surface secondary rough polishing in S5, a rough polishing grinding tool with lower Brinell hardness and high heat conductivity coefficient and a fine grain size rough polishing grinding material are adopted, so that the irregular surface shape of the spherical surface after the spherical surface is finely ground in S3 can be quickly repaired, the bulge of a 60-degree circular ring region in the optical axis direction can be quickly removed in a short time, the ball milling and fine polishing time is shortened, the subsequent S6 spherical surface fine polishing process does not need to consume a large amount of time to repair the surface shape precision, meanwhile, the surface defect grade B of the large-caliber sapphire spherical surface after the two-time rough polishing can be promoted to be less than or equal to VI grade, the processing time of the S6 spherical surface fine polishing process is favorably shortened, the processing cost is reduced, and the polishing efficiency is improved.
In the twice rough polishing scheme with optimized process conditions, the method is more favorable for reducing the surface roughness Ra of the S3 spherical surface after fine grinding, improving the grade B of surface defects, controlling the number N of surface shape f-turns and the local error delta N of the aperture, meeting the high index requirement of the polished finished product, and avoiding long-time polishing to improve the grade B of the surface defects, control the number N of the surface shape f-turns and the local error delta N of the aperture. In some embodiments, the comparison of multiple process data reveals that: the time for fine grinding of the spherical surface is reduced by 2-3h compared with the conventional classical processing technology, and the time for fine polishing of the spherical surface is reduced by 70-75h compared with the conventional classical processing technology.
In the rough polishing grinding tool scheme with the optimized size and structure, the large-caliber sapphire spherical crystal part with the surface defect grade B less than or equal to VI, the surface shape diaphragm number N less than or equal to 5 and the diaphragm local error of 0.5 less than or equal to delta N less than or equal to 1 can be provided for subsequent spherical surface fine polishing, so that the processing efficiency of the subsequent spherical surface fine polishing is improved, the processing period of the spherical surface fine polishing is shortened, and the processing cost is reduced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
Figure 1 is a top view of a concave or convex spherical abrasive article.
Figure 2 is a cross-sectional view of a convex spherical abrasive tool.
Figure 3 is a cross-sectional view of a concave spherical grinding tool.
Fig. 4 is a schematic view of a structure of ingot slicing.
Description of the reference numerals
1. A ring groove, 2, a vertical groove, 3, a second crystal ingot, 4, a crystal ingot bottom.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and these ranges or values should be understood to encompass values close to these ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The terms interpretation and test methods in the present invention:
a spherical crystal refers to a sapphire crystal product obtained by growing a crystal, milling the grown crystal into a spherical surface, and performing spherical coarse grinding, spherical fine grinding, and polishing (including rough polishing and polishing) to obtain a spherical surface (or referred to as a cambered surface), for example, a sapphire ball cover. It does not refer to individual crystals. The intermediate product in the intermediate processing of the spherical rough grinding, spherical fine grinding and polishing treatment (including rough polishing and fine polishing) is called sapphire spherical surface.
Dislocation density, which is the total length of dislocation lines contained in a unit volume of crystal, in ps/cm 2 . The dislocation density is obtained by testing by a corrosive metallographic method according to reference GB/T33763-2017.
The single crystallinity means that particles in the crystal are regularly and periodically arranged in a three-dimensional space, or the whole crystal is composed of the same spatial grid in the three-dimensional direction, and the long-range order of mass points in the whole crystal in the spatial arrangement is used for representing the growth quality of the crystal; the smaller the value, the smaller the lattice distortion. The X-ray diffraction spectrum analyzer is obtained through XRD test, is a half-height width (half-peak width) numerical value of an XRD rocking curve, has the unit of arc seconds, and is used for reflecting the dispersion condition of a diffraction beam of an X-ray after being reflected by a crystal face to be detected, so that the growth quality of the crystal to be detected is represented, and the smaller the half-height width is, the better the crystal quality is, and the worse the crystal quality is.
And the surface defect grade B is that the surface defects comprise scratches and pocks, the surface defects are divided into 10 grades (0, I-10, I-20, I-30, II, III, IV, V, VI and VII), and the specific judgment is carried out according to the national standard GB1185-74. The invention uses an image measuring instrument to measure scratches and pits.
The surface-shaped f-number N is the number of interference fringes (apertures) generated when the curvature radius of the surface of the detected spherical surface is deviated from the curvature radius of the standard surface of the standard template when the surface of the optical part (sapphire spherical crystal or sapphire spherical surface) is detected, and the newton interference ring is generally represented by N. The method is characterized in that a spherical working sample plate (copied by a spherical standard sample plate, referred to GB/T1240-76 and used for checking and processing parts) is used for measurement, the f-number of the spherical working sample plate is based on 546nm monochromatic light, the room temperature is kept at 20 +/-3 ℃ during measurement, the spherical curvature radius (namely the spherical working sample plate curvature radius) is referred to the spherical standard surface curvature radius, the spherical working sample plate is placed on a detected spherical surface, and the number of interference fringes (apertures) generated when the spherical working sample plate surface curvature radius is deviated from the detected spherical surface curvature radius, namely the surface shape f-number N, is obtained.
The aperture local error delta N is the degree of local irregularity of interference fringes generated between the surface of the detected spherical surface and the surface of the reference spherical working template when the aperture error of the surface shape of the part is detected by applying the principle of light interference under the measurement of the optical working template. The measurement of the aperture local error Δ N is a ratio of a deviation of the local irregular interference fringes of the detected spherical surface to the ideal smooth interference fringes to a distance between two adjacent fringes, and takes a maximum value, that is, Δ N = the deviation/the distance between two adjacent fringes.
The invention provides a preparation method of a sapphire spherical crystal, which comprises the steps of sapphire crystal growth and sapphire crystal polishing and forming, wherein the sapphire crystal growth step comprises the steps of loading, thermal field assembly, heating and raw material meltingMelting, adjusting the liquid level temperature, seeding and growing, wherein the seeding and growing process comprises the following steps: putting the seed crystal downwards, touching the seed crystal with the liquid surface at the speed of 1.5-3mm/min, observing the weight change of the seed crystal through a weighing system after touching the liquid surface, starting to grow the crystal by adjusting the power for growth or melting and adjusting the flushing amount of argon introduced above to be 2-20L/min until the weight of the seed crystal is stable, then starting to reduce the power after stabilizing for 1-3h, starting to grow the crystal, cooling after the crystal growth process is finished, and ensuring that the dislocation density of the obtained sapphire single crystal is less than or equal to 1100ps/cm 2 The single crystallinity according to XRD test is less than or equal to 14 arcsec; and the polishing and forming steps of the sapphire crystal comprise: s1, milling and grinding, S2, roughly grinding the spherical surface, S3, finely grinding the spherical surface, S4, roughly polishing the spherical surface for the first time, S5, roughly polishing the spherical surface for the second time, and S6, finely polishing the spherical surface.
The specific processes of charging, thermal field assembly, heating, raw material melting, and liquid level temperature adjustment according to the present invention can be performed according to methods known in the art, for example, in the applicant's earlier patents CN102383187B and CN103060913B.
The type and shape of the raw materials used in the sapphire crystal growth step of the present invention may be any of those existing in the art, and those skilled in the art may select them as desired; as the kind of the raw material, for example, 99.999wt% of high purity alumina can be used, and the raw material can be in the form of, for example, a cake (having a size of, for example, 40 to 80mm in diameter) and/or a particle (e.g., a regular shape and/or an irregular shape).
The thermal field assembly according to the present invention includes adjusting and installing the heater and the thermal field, which is the prior art and will not be described herein. In the present invention, it should be understood that the argon introduced above refers to high purity argon introduced through a tungsten tube above a crucible for loading materials, which is a conventional means in the art and will not be described herein.
It is understood that the maintaining of the weight of the seed crystal stable in the present invention means that the seed crystal is in a stable state of insoluble and non-growing, and the weight of the seed crystal is stable and unchanged.
The crystal ingot obtained in the sapphire crystal growing step is a C-direction sapphire crystal ingot.
In some preferred embodiments, as shown in fig. 4, the preparation method further comprises: before the step of polishing and shaping the sapphire crystal, carrying out first segmentation on the bottom 4 of the ingot obtained in the step of growing the sapphire crystal at a position 200-250mm above the bottom to obtain a first upper ingot; and performing second segmentation at the position 130-180mm above the bottom of the first ingot to obtain a second ingot 3, wherein the second ingot 3 is used as a raw material in the sapphire crystal polishing and forming step. Under the preferred scheme, the second crystal ingot can be ensured to have no bubbles and no stress and the purity is more than or equal to 99.999wt%, because bubbles or fog-like bubbles with different degrees can appear at the contact position with the seed crystal in the initial crystal growth process in the sapphire crystal growth step, the bubble content at the top end of the crystal is more, impurities in the raw material can gradually sink into the bottom of the crucible in the raw material melting process, so the impurities at the bottom of the crystal are more, and the second crystal ingot is taken as the raw material in the sapphire crystal polishing and forming step, thereby being more beneficial to reaching the crystal raw material index required by the sapphire spherical crystal finished product.
The first and second cuts may be made in cutting equipment known in the art, such as a single wire cutter.
Those skilled in the art can also perform other conventional operations according to actual needs, such as determining the crystal axis direction of the obtained ingot (which may be the ingot obtained by the growth process, or the second ingot obtained by the second division process), and for example, placing the obtained ingot on an 8BD orienter platform, determining the crystal axis direction of the ingot by using an 8BD orienter: the C direction is less than or equal to 1 degree. For another example, after the ingot is processed, the ingot is machined (e.g., bar-cutting, grinding, etc.) to obtain the raw material for the sapphire crystal polishing and shaping step of the desired shape.
The milling and grinding in the invention S1 can be performed by methods of the prior art, and are not described herein again.
In some preferred embodiments, S2 the spherical rough grinding and S3 the spherical finish grinding each independently satisfy: the Brinell hardness of the adopted grinding tool is 100-270N/mm 2 The heat conductivity coefficient of the grinding tool is less than 45W/(m.K); and/or the particle size of the adopted coarse grinding abrasive is 90-110 mu mThe grain size of the fine grinding abrasive is 20-30 μm. Under the preferred scheme of the invention, the high-hardness grinding tool and the grinding material with proper particle size are adopted to carry out the spherical surface rough grinding in the step S2 and the spherical surface finish grinding in the step S3, so that the grinding speed is improved, and particularly, the high-hardness grinding tool is wear-resistant, is beneficial to accelerating the grinding speed and has low cost; meanwhile, the proper abrasive particle size range is controlled, so that the sapphire spherical surface can be prevented from being scratched by a high-hardness grinding tool as far as possible. Under the same condition, if the abrasive is lower than the particle size range, although the 60-degree annular region in the direction of the spherical optical axis is small in projection, the possibility of scratching is generated; if the particle size is higher than the above range, the sapphire spherical surface roughness is relatively large (e.g., ra 0.5-0.6 μm), which may increase the post-processing time and cause problems such as over-polishing.
The specific type of the abrasive tool of the present invention may be any tool that satisfies the above-mentioned brinell hardness and thermal conductivity, and may be, for example, a high-hardness abrasive tool such as cast iron. The specific type of the corresponding abrasive is not particularly limited as long as it satisfies the above particle diameter in the art, and examples thereof include abrasives such as boron carbide.
In some preferred embodiments, the process of spherical rough grinding described in S2 controls the roughness Ra of the obtained sapphire spherical surface to be 1-1.2 μm, and the process of spherical fine grinding described in S3 controls the roughness Ra of the obtained sapphire spherical surface to be 0.25-0.35 μm. The optimized scheme is more beneficial to shortening the processing time of the next procedure (twice rough polishing).
Preferably, the preparation method further comprises the following steps: and (4) cleaning the sapphire spherical surface obtained by fine grinding of the spherical surface in the step (S3), measuring the curvature radius of the sapphire spherical surface by using a sphere diameter instrument, and reserving a rough polishing allowance (the rough polishing allowance is preferably 0.03-0.05 mm) for the primary rough polishing of the spherical surface in the step (S4). Under this preferred scheme, can be more accurate through S4 the sphere once rough throw S3 the destruction layer that the sphere finish grinding produced is got rid of, more does benefit to and reduces process time.
The inventor of the invention further researches and discovers that after the spherical surface is finely ground, a 60-degree circular ring area in the direction of the optical axis of the sapphire spherical surface is protruded, so that the surface shape is irregular; the surface shape of the sapphire is controlled by adopting a classical polishing process to avoid sapphireThe polishing quality is affected by the problems of polishing scratch, over-polishing and the like caused by the fact that protrusions appear in a 60-degree circular ring area in the direction of a spherical optical axis of the spherical surface during polishing, a fine-grain abrasive soft grinding tool needs to be used for polishing for a long time, when the sapphire spherical surface is polished, the 60-degree circular ring area in the direction of the spherical optical axis of the sapphire is polished firstly, one of the characteristics of the sapphire is high in hardness, the polishing removal amount is limited, the number N of surface-shaped diaphragms is difficult to rapidly enable to be less than or equal to 5, the local error delta N of the diaphragms is less than or equal to 0.5, the spherical surface cannot be uniformly polished, and the surface quality cannot reach the surface defect grade B which is less than or equal to IV. In the prior art, the surface shape of the spherical surface is modified by classical polishing for a long time, and then the spherical surface is uniformly polished after being modified to be regular, so that the surface defect grade B is not more than IV grade, the surface shape aperture number N is not more than 5, and the aperture local error delta N is not more than 0.5. In this regard, in some preferred embodiments of the present invention, the spherical primary rough polishing of S4 and the spherical secondary rough polishing of S5 each independently satisfy: the Brinell hardness of the adopted rough polishing grinding tool is 35-50N/mm 2 The coefficient of thermal conductivity of the rough polishing grinding tool is more than 350W/(m.K), and/or a polishing solution containing a rough polishing grinding material is adopted, and the grain diameter of the rough polishing grinding material is not more than 2.5 mu m, and is preferably less than 1 mu m. In the preferred scheme of the invention, a medium-hardness rough polishing grinding tool with small hardness and high heat conductivity coefficient is adopted, and a suitable small-particle-size rough polishing abrasive polishing solution is preferably matched, so that the short-time removal of the bulge in the 60-degree circular ring area in the optical axis direction is realized, and the ball-milling fine polishing time is shortened; meanwhile, the quality of the sapphire spherical crystal is improved.
In some more preferred embodiments, S2 the spherical rough grinding and S3 the spherical finish grinding each independently satisfy: the Brinell hardness of the adopted grinding tool is 100-270N/mm 2 The heat conductivity coefficient of the grinding tool is less than 45W/(m.K); the grain size of the adopted coarse grinding material is 90-110 mu m, and the grain size of the adopted fine grinding material is 20-30 mu m; the S4 spherical surface primary rough polishing and the S5 spherical surface secondary rough polishing respectively and independently meet the following requirements: the Brinell hardness of the adopted rough polishing grinding tool is 35-50N/mm 2 The heat conductivity coefficient of the rough polishing grinding tool is larger than 350W/(m.K), and a polishing solution containing rough polishing grinding materials is adopted, wherein the grain diameter of the rough polishing grinding materials is smaller than 1 mu m. Under this preferred scheme, more do benefit to and avoid fish tail heavy-calibre sapphire spherePossibly, the surface defect grade B of the large-caliber sapphire sphere is improved; the grinding tool for roughly grinding the spherical surface and finely grinding the spherical surface has better buffering performance, can effectively disperse the impact force of the spherical surface in the processing process of removing the bulge in the 60-degree annular region in the direction of the spherical optical axis in a short time, and simultaneously has a large heat conductivity which is far higher than that of the high-hardness grinding tool adopted in the S2-S3, so that the heat generated in the processing process can be quickly transferred, the spherical surface irregularity caused by the thermal deformation of the grinding tool and the sapphire spherical surface is avoided, the bulge in the 60-degree annular region in the direction of the spherical optical axis can be quickly removed in a short time, the total processing time of the S3-S6 is shortened, and the polishing efficiency is better improved.
The specific type of the rough polishing grinding tool in the present invention is not limited as long as it satisfies the above brinell hardness and thermal conductivity, and is preferably a grinding tool having a high purity and a very small content of impurities, and for example, a grinding tool such as red copper may be preferable. The specific type of the rough polishing abrasive is only required to be an abrasive satisfying the above particle size in the art, and for example, an abrasive such as diamond may be preferable.
In a preferred embodiment, a cast iron grinding tool is used for the rough spherical grinding and the fine spherical grinding of S2 and a copper grinding tool (preferably red copper) is used for the rough spherical polishing of S4 and the rough spherical polishing of S5. Under this preferred scheme, adopt the soft copper grinding apparatus of texture than the cast iron grinding apparatus, more do benefit to the impact force of effectual dispersion sphere, and be difficult for fish tail sapphire sphere.
Further preferably, the rough polishing grinding tool comprises a concave spherical grinding tool for rough polishing of the convex surface of the sapphire spherical surface and a convex spherical grinding tool for rough polishing of the concave surface of the sapphire spherical surface, as shown in fig. 1, fig. 2 and fig. 3, a plurality of circular grooves 1 and a plurality of vertical grooves 2 are respectively formed in the concave spherical surface of the concave spherical grinding tool and the convex spherical surface of the convex spherical grinding tool, the circular grooves 1 are used for distributing polishing liquid, and the vertical grooves 2 are used for guiding external air into the space between the rough polishing grinding tool and the sapphire spherical surface. Under the preferred scheme of the invention, the arranged circular ring groove can effectively distribute the polishing solution, reduce the loss of the polishing solution and reduce the cost; the polishing solution in the circular groove can be uniformly distributed at any position of the sapphire spherical surface in the swinging process of the rough polishing grinding tool and the rotating process of the workpiece spindle, so that the sapphire spherical surface is ground more uniformly, and the surface shape precision is higher; meanwhile, the vertical groove can guide external air into the space between the rough polishing grinding tool and the sapphire spherical surface, so that the air can fully and quickly reach the sapphire spherical surface in the twice rough polishing process, and the damage to the large-caliber sapphire spherical surface during the separation of the rough polishing grinding tool and the sapphire spherical surface is reduced.
In the present invention, it should be understood that when the rough polishing grinding tool is applied, the concave spherical grinding tool can be used to process the convex sapphire surface, and then the convex spherical grinding tool can be used to rough polish the concave sapphire surface. It should be understood that the concave spherical grinder and the convex spherical grinder are sized to match the radii of curvature of the convex and concave surfaces of the sapphire spheres, respectively, for grinding thereof.
The circular groove and the vertical groove are mutually crossed and communicated. Preferably, the circular grooves are arranged at intervals in a concentric circular ring mode by taking a central point of the concave spherical grinding tool or the convex spherical grinding tool as a center. Preferably, the vertical groove penetrates through the circular grooves and is communicated with the circular grooves. The vertical slots may or may not be located on a radius of the corresponding spherical surface. More preferably, the plurality of vertical slots are symmetrically distributed along a central point of the corresponding abrasive tool. Under the preferred scheme of the invention, the circular grooves and the vertical grooves are reasonably distributed, so that the adverse effects caused by stress damage and heat accumulation when the circular ring area is bulged in the direction of the optical axis of the sapphire sphere for two times of rough polishing can be further avoided; the annular groove can realize radial interval distribution of the polishing solution and the rough polishing grinding tool and flow of the polishing solution in the circumferential direction, is more beneficial to uniform distribution of the polishing solution, is more beneficial to uniformly mixing worn particles and unworn particles of a rough polishing grinding material in the polishing solution, and ensures consistent polishing degree; air is introduced into the vertical grooves, so that the conduction of force and the conduction of heat are effectively isolated, the problems of damage, heating, adhesion and the like of the sapphire spherical surface can be further reduced, and the safe use of the rough polishing grinding tool in the two rough polishing processes can be further ensured.
More preferably, the groove widths of the circular ring grooves and the vertical grooves are each independently 1-4mm, such as 1, 1.5, 2, 2.5, 3, 3.5, 4mm, etc.; the groove depths are each independently 1 to 6mm, specifically, for example, 1, 2, 3, 4, 5, 6mm, etc. Under this preferred scheme, the groove width, the groove depth are suitable, more do benefit to the ring groove that sets up suitable quantity, more do benefit to the evenly distributed of polishing solution at the sphere, reduce the polishing solution cost simultaneously.
More preferably, the groove width and the groove depth of the vertical groove are respectively greater than the groove width and the groove depth of the circular ring groove, that is, the groove width of the vertical groove is greater than the groove width of the circular ring groove, and the groove depth of the vertical groove is greater than the groove depth of the circular ring groove. Under this preferred scheme, more do benefit to and shorten total process time, promote the final gained sapphire spherical crystal quality.
The width and depth of the circular ring groove or the vertical groove can be the same or different, preferably, the width and depth of the circular ring groove are the same, and the width and depth of the vertical groove are the same.
More preferably, the sum of the slotted areas of the circular ring groove and the vertical groove in the concave spherical grinding tool is 1/5-3/10 of the area of the concave spherical surface, and the sum of the slotted areas of the circular ring groove and the vertical groove in the convex spherical grinding tool is 1/5-3/10 of the area of the convex spherical surface. Under the optimized scheme, the grooving area is appropriate, so that the contact surface between the rough polishing grinding tool and the sapphire spherical surface is appropriate and large, the grinding area is appropriate and large, and the grinding efficiency is more favorably improved; meanwhile, the polishing solution has good fluidity, so that the distribution uniformity of the polishing solution is improved, and the polishing efficiency and quality are improved.
More preferably, the plurality of circular grooves are arranged at equal intervals, and the plurality of vertical grooves are arranged at equal intervals. Under the preferred scheme, the polishing solution is more favorably and uniformly distributed and external air is introduced, so that the rough polishing effect is more favorably improved; the problems of contact surface reduction, insufficient grinding amount, uneven grinding of the spherical surface and the like caused by the fact that the convex positions of the 60-degree circular ring area in the optical axis direction of the sapphire spherical surface are arranged in more dense grooves can be avoided as much as possible.
Those skilled in the art can determine the number of the circular ring grooves and the vertical grooves, and the groove depth and the groove width according to the above-mentioned grooving area, the distribution of the polishing liquid, and the introduction of the external air. For example, 1-4mm (groove width) × 1-4mm (groove depth) circular grooves and 2-6 symmetrical 2-6mm vertical grooves are arranged on the rough polishing grinding tool at intervals of 2-6mm, so that the polishing solution is uniformly distributed on the sapphire spherical surface, and the processing efficiency is improved.
In some preferred embodiments, the spherical primary rough polishing in S4 and the spherical secondary rough polishing in S5 are both performed on a grinding machine, and the spindle rotation speed and the pendulum axis pendulum speed of the grinding machine in the spherical secondary rough polishing are both controlled to be higher than those of the spherical primary rough polishing, and/or the pendulum axis pressures of the spherical primary rough polishing in S4 and the spherical secondary rough polishing in S5 are each independently 0.05 to 0.15MPa, preferably 0.1 to 0.15MPa.
The grinding machine may be any known apparatus in the art, and it should be understood that it has a main shaft, a pendulum shaft, which enables the main shaft to swing while the pendulum shaft is rotating, for example, a single shaft grinding machine, or a double pendulum machine as in CN 106736875B.
More preferably, the process conditions of the first rough polishing of the spherical surface in S4 include: controlling the rotation speed of a main shaft to be 10-30rpm, the swing speed of a swing shaft to be 15-25rpm, and the pressure of the swing shaft to be 0.05-0.15MPa, and/or controlling the surface shape f-number N of the sapphire spherical surface to be less than or equal to 5, and the local error delta N of the aperture to meet the condition that delta N is less than or equal to 1 and is greater than or equal to 0.5. Under this preferred scheme, adopt lower rotational speed, slew velocity, can make the rough polishing abrasive material have longer time and obtain fully grinding on the sapphire sphere, more do benefit to and realize the effect that 60 rings region bulges in optical axis direction are got rid of fast to the preferred under the circumstances of avoiding the sapphire fish tail, more do benefit to and improve the local error delta N of diaphragm and the face shape diaphragm number N fast.
More preferably, the process conditions of the spherical surface secondary rough polishing in S5 include: the rotating speed of a main shaft is controlled to be 30-50rpm, the swing speed of a swing shaft is controlled to be 20-40rpm, the pressure of the swing shaft is controlled to be 0.05-0.15MPa, and/or the surface defect grade B of the sapphire spherical surface is controlled to be less than or equal to VI grade, the surface shape diaphragm number N is controlled to be less than or equal to 5, and the local error delta N of the diaphragm satisfies that delta N is greater than or equal to 0.5 and less than or equal to 1. Under the preferred scheme, the rough polishing grinding tool can move back and forth on the sapphire spherical surface more quickly at higher rotating speed and swing speed, so that the surface quality and the surface defect grade B can be improved by accelerating the speed; meanwhile, the deformation of the surface-shaped aperture caused by excessive stay of the rough polishing grinding tool at the same position is avoided.
In some more preferred embodiments of the present invention, the process conditions of the spherical surface primary rough polishing in S4 include: controlling the rotation speed of a main shaft to be 10-30rpm, the swing speed of a swing shaft to be 15-25rpm, and the pressure of the swing shaft to be 0.05-0.15MPa, and/or controlling the surface shape f-number N of the sapphire spherical surface to be less than or equal to 5, and the local error delta N of the aperture to meet the condition that delta N is less than or equal to 1 and is greater than or equal to 0.5; s5, the process conditions of the secondary rough polishing of the spherical surface comprise: the rotating speed of a main shaft is controlled to be 30-50rpm, the swing speed of a swing shaft is controlled to be 20-40rpm, the pressure of the swing shaft is controlled to be 0.05-0.15MPa, and/or the surface defect grade B of the sapphire spherical surface is controlled to be less than or equal to VI grade, the surface shape diaphragm number N is controlled to be less than or equal to 5, and the local error delta N of the diaphragm satisfies that delta N is greater than or equal to 0.5 and less than or equal to 1. Under the preferred scheme, the spherical surface primary rough polishing can quickly and uniformly grind the 60-degree circular ring region in the optical axis direction, the spherical surface secondary rough polishing is more favorable for S5 to quickly grind the sapphire spherical surface at higher rotating speed and swing speed under the condition of not scratching the sapphire spherical surface, the grinding stress is uniform, and the speed is accelerated to realize the improvement of the surface quality and the surface defect grade B.
After the spherical surface primary rough polishing in the S4 and the spherical surface secondary rough polishing in the S5, the surface roughness Ra of the spherical surface after the spherical surface fine grinding in the S3 can be quickly reduced, the surface defect grade B is improved, the surface shape f-number N and the aperture local error delta N are controlled, the requirement of a finished polished product is met, and the surface defect grade B is not required to be improved, and the surface shape f-number N and the aperture local error delta N are not required to be controlled by the spherical surface fine polishing in the S6 for a long time.
In some preferred embodiments, the spherical fine polishing at S6 satisfies: adopting polishing solution containing fine polishing abrasive with the grain diameter of 500-1000nm. Under the optimized scheme, the fine polishing grinding material with a fine grain diameter is adopted, the generated grinding physical effect is small, the removal amount is small, the surface smoothness of the optical-grade sapphire spherical crystal part can be further refined and improved, the local error delta N of the aperture is reduced, the surface shape f-number N is reduced, the surface defect grade B and the surface shape precision of the optical-grade sapphire spherical crystal part are further improved, the surface shape f-number N of the sapphire spherical crystal can be enabled to be less than 5, and the surface shape precision is better when the f-number is smaller.
The fine polishing grinding tool for the spherical fine polishing can be made of materials conventionally adopted in the prior art, such as an asphalt grinding tool (preferably polishing asphalt which is pressed into a required grinding tool in a semi-solid form according to the curvature radius of a part, and the preferred melting point of the polishing asphalt is 60-70 ℃).
The type of the finish polishing abrasive is not particularly limited as long as it satisfies the above particle size in the art, and examples thereof include abrasives such as alumina.
The polishing agent types and solid contents of the polishing solutions adopted in S4-S6 in the invention can be carried out conventionally in the field, and can be used in the invention; for example, the polishing solution of S4-S5 may have a solid content of 0.5-3wt% and the polishing solution of S6 may have a solid content of 10-20wt% of the corresponding abrasive. The skilled person can select the invention according to the actual requirement and can achieve the effect of the invention.
In some preferred embodiments, the spherical surface finish polishing in S6 is performed on a polishing machine, and the process conditions thereof include: controlling the rotation speed of a main shaft of the polishing machine to be 50-150rpm, preferably 80-120rpm, the swing speed of a swing shaft to be 20-40rpm, and the pressure of the swing shaft to be 0.05-0.15MPa, and/or controlling the surface defect grade B of the sapphire spherical crystal to be less than or equal to IV grade, the surface shape f-number N to be less than or equal to 5, and the local error delta N of the aperture to be less than or equal to 0.5. Under the optimal scheme, the appropriate rotating speed and the appropriate swing speed are adopted, the surface shape precision of the optical-grade sapphire spherical crystal is improved, and meanwhile, the surface defect grade B of the optical-grade sapphire spherical crystal part is slowly improved.
More preferably, the spherical surface finish polishing of S6 is performed on a polishing machine, and the process conditions include: controlling the rotation speed of a main shaft of the polishing machine to be 80-120rpm, the swing speed of a swing shaft to be 20-40rpm, controlling the pressure of the swing shaft to be 0.05-0.15MPa, controlling the surface defect grade B of the sapphire spherical crystal to be less than or equal to the grade IV, controlling the surface shape diaphragm number N to be less than or equal to 5, and controlling the local error delta N of the diaphragm to be less than or equal to 0.5. Under the preferred scheme, the quality of the optical-grade sapphire spherical crystal part can be controlled to meet the requirement in a shorter time. Under the same condition, if the speed of the main shaft is too high, the surface defect grade B is increased to B which is less than or equal to IV, but the trimming of the aperture local error delta N is slowed down, and the time for trimming the aperture local error delta N is required to be increased; too low a swing speed can result in too slow a promotion of the surface defect grade B, and the fine polishing time can be prolonged.
In the present invention, a person skilled in the art may perform other conventional operations according to actual requirements, for example, in the spherical surface finish polishing described in S6, a person skilled in the art may take down the sapphire spherical crystal part at regular intervals (for example, 1 to 2 hours) to detect the surface shape accuracy and the surface defects. For another example, in the preset grinding size of each step, enough grinding allowance is set for the next process so as to remove a damaged layer or a sand surface generated by the previous process, so that the sand surface of the whole sapphire spherical crystal is consistent.
The size of the sapphire spherical crystal part can be selected by a person skilled in the art according to actual requirements, and can be, for example, the total height is 20-164mm, the center thickness is 3-150mm, the diameter of an excircle is 100-300mm, the curvature radius of a spherical convex surface is 50-2000mm, and the curvature radius of a spherical concave surface is 45-2000mm.
In some embodiments, compared to the classical large-caliber sapphire spherical crystal polishing process in the prior art, the preparation method of the present invention uses the following steps in table 1 and table 2 respectively in multiple processing, and it can be seen that the preparation method of the present invention can significantly improve the processing efficiency, especially shorten the processing cycle of S6 spherical fine polishing and reduce the processing cost.
Table 1: processing time of classical large-caliber sapphire spherical crystal polishing process
Table 2: the preparation method of the sapphire spherical crystal has the processing time
The present invention is further illustrated in detail below with reference to specific examples.
Example 1
A preparation method of a sapphire spherical crystal comprises the following specific steps:
1. using 99.999wt% of high-purity alumina, round cake with 50mm diameter and inevitable partial irregular-shaped particlesFilling, adjusting and installing a heater and a thermal field, heating, melting raw materials, adjusting the temperature of a liquid surface, putting seed crystals down, touching the seed crystals on the liquid surface at a speed of 2mm/min, observing the weight change of the seed crystals through a high-precision weighing system after touching the liquid surface, adjusting the power of growth or melting and adjusting the high-purity argon gas introduced above the seed crystals to be in a 15L/min state until the weight of the seed crystals is kept stable, the seed crystals are in an insoluble and non-growing state, then starting to reduce the power after 2 hours of stability, starting to grow the crystals, growing the neck, growing the shoulder, waiting for the growth of the neck, cooling, taking the crystals, and detecting the crystals. The obtained crystal has no obvious defects by visual observation, few bubbles and small stress, and the purity is more than or equal to 99.999wt percent and is a C-direction sapphire crystal ingot. By detecting that the dislocation density of the crystal is less than or equal to 1100ps/cm 2 The monocrystallinity according to XRD test is less than or equal to 14 arcsec.
2. The obtained ingot is placed on an 8BD orientation platform, and the crystal axis direction of the ingot is measured by using the 8BD orientation platform: the C direction is less than or equal to 0.5 degree and is adhered to the iron plate.
3. Placing the oriented ingot on a single wire cutting machine platform, and performing first segmentation from the bottom of the ingot to a position 220mm upwards by using a single wire cutting machine to obtain a first ingot above the ingot; and performing second segmentation on the bottom of the first ingot to the position 155mm above the bottom of the first ingot to obtain a second ingot below the bottom of the first ingot. The feedstock is selected from a second ingot.
4. The second ingot cut by the single wire cutter was reoriented using an 8BD orienter: bonding the C direction to be less than or equal to 0.5 degree on an iron disc, and then using a machining center to select a bar digging drill with the diameter of 160mm for digging bars.
5. A round bar with the diameter of 153mm is fixed on an ejector pin excircle grinding machine, and the diameter of the raw material is ground to 2mm by using the ejector pin excircle grinding machine.
6. And (3) fixing the bar stock ground by the thimble outer circle grinding machine on a single-wire cutting machine, and cutting the raw material into crystal blocks with the length of 77mm by using the single-wire cutting machine again.
7. And fixing the cut crystal blocks on a platform of a plane grinding machine, and grinding the end surface of the raw material by using the plane grinding machine by 0.5mm.
8. Fixing the crystal blocks processed by a plane grinding machine on a workpiece shaft of a ball mill, then milling and grinding raw materials into a large-caliber sapphire spherical blank by using the ball mill and selecting a 60# milling and grinding wheel: the total height is 76.5mm, the center thickness is 7mm, the curvature radius of the spherical convex surface is 78mm, and the curvature radius of the spherical concave surface is 67mm.
9. The large-caliber sapphire spherical polishing and milling piece is fixed on a workpiece shaft of a single-shaft grinding machine, the single-shaft grinding machine is used, a cast iron grinding tool is selected, a boron carbide grinding material with the grain size of 90-110 mu m is selected, spherical coarse grinding is carried out, a large-caliber sapphire spherical blank reaches the total height of 76mm, the center thickness of the large-caliber sapphire spherical blank reaches 6mm, the curvature radius of a convex surface of the large-caliber sapphire spherical blank reaches 76mm, the curvature radius of a concave surface of the large-caliber sapphire spherical blank reaches 69mm, and the roughness Ra of the obtained sapphire spherical surface is 1.2 mu m.
10. Fixing the large-caliber sapphire spherical polishing rough grinding piece on a workpiece shaft of a single-shaft grinding machine, using the single-shaft grinding machine, selecting a cast iron grinding tool, selecting a boron carbide grinding material with the particle size of 20-30 mu m, and carrying out spherical finish grinding to enable the large-caliber sapphire spherical blank to reach the total height of 75.5mm, the center thickness of 5.1mm, the curvature radius of a convex surface of the spherical blank to be 75.05mm and the curvature radius of a concave surface of the spherical blank to be 69.95mm. The roughness Ra of the obtained sapphire spherical surface was 0.30. Mu.m.
11. According to the size of the large-caliber sapphire spherical crystal, designing a matched spherical grinding tool made of red copper: concave spherical grinding tools and convex spherical grinding tools.
12. On the mill face of concave sphere grinding apparatus and convex sphere grinding apparatus, every 4mm car 2mm's a plurality of concentric circles's of diameter direction along the sphere of corresponding grinding apparatus round ring groove and along the sphere centrosymmetric 4mm 4mm perpendicular groove of corresponding grinding apparatus, 4 perpendicular grooves wholly are the cross, perpendicular groove runs through the ring groove and is linked together, fluting area sum is 1/5 of corresponding mill face sphere area. This will be favorable to polishing solution evenly distributed on heavy-calibre sapphire sphere, promotes machining efficiency.
13. The polishing solution for the two rough polishing processes is diamond polishing solution with the grain diameter less than 0.5 mu m, wherein the solid content of diamond is 2wt%.
14. Cleaning the finished large-caliber sapphire spherical surface after the spherical surface is finely ground, measuring the spherical surface by using a sphere diameter instrument, and measuring the actual value of the curvature radius of the convex surface of the spherical surface to be 75.05mm and the actual value of the curvature radius of the concave surface of the spherical surface to be 69.95mm, wherein the actual values are close to the curvature radius R =75mm of the convex surface of the standard spherical surface for finely grinding the spherical surface and the curvature radius R =70mm of the concave surface of the standard spherical surface; and then clamping the diamond rough polishing solution on a single-shaft grinding machine, carrying out one-time rough polishing on the spherical surface by using a spherical surface grinding tool and the diamond rough polishing solution, and controlling the rotating speed of a main shaft to be 20rpm, the swinging speed of a pendulum shaft to be 20rpm, the pressure to be 0.1MPa and the processing time to be 10min. At the moment, a 60-degree circular ring convex area in the direction of the spherical optical axis of the large-caliber sapphire sphere is quickly and uniformly ground, a part is taken down and cleaned, and the spherical working sample plate is used for measurement, so that the number N of surface-shaped diaphragms is determined to be 5, and the local error delta N of the diaphragms is determined to be 0.86.
15. And (3) re-clamping the large-caliber sapphire spherical surface obtained by the primary rough polishing of the spherical surface on a single-shaft grinding machine for secondary rough polishing of the spherical surface, adjusting the rotating speed of a main shaft to 40rpm, adjusting the swinging speed of a swing shaft to 30rpm, adjusting the pressure to 0.1MPa, processing for 20min, controlling an aperture, simultaneously improving the surface quality, taking down the part after the completion, and measuring by using an image measuring instrument and a working sample plate to determine that the grade B of the surface defect is VI grade, the number N of turns of the surface-shaped aperture is 4 and the local error delta N of the aperture is 0.75.
16. Clamping the large-caliber sapphire spherical surface obtained by the secondary rough polishing of the spherical surface on a polishing machine, performing spherical surface fine polishing, adopting polishing asphalt as a fine polishing grinding tool, adopting an alumina polishing solution with the particle size of 700-900nm as a fine polishing grinding material, wherein the solid content of alumina in the polishing solution is 15wt%, adjusting the rotation speed of a main shaft to 100rpm, adjusting the swing speed of a pendulum shaft to 30rpm and the pressure to 0.1MPa, taking down the part for detection every 1h, recording data, and detecting the large-caliber sapphire spherical crystal part within 10h to reach an index: the surface defect grade B is IV grade, the surface shape diaphragm number N is 3, and the diaphragm local error delta N is 0.4.
The processing time for each step is shown in table 3 below.
Example 2
The method of example 1 was followed, except that the vertical grooves in the concave spherical grinders and the convex spherical grinders had a groove width and a groove depth of 2mm × 2mm, which were the same as those of the circular grooves. The processing time of each step is shown in table 3; the surface shape f-number N of the sapphire spherical surface obtained after the spherical surface is roughly polished for one time is 5, and the local error delta N of the aperture is 0.95; the surface defect grade B of the sapphire spherical surface obtained after the secondary rough polishing of the spherical surface is more than VI grade, the surface shape f-number N is 5, and the local error delta N of the aperture is 0.8; the surface defect grade B of the sapphire spherical crystal obtained by spherical fine polishing for 30h is grade IV, the surface shape diaphragm number N is 4, and the diaphragm local error delta N is 0.45.
Example 3
The process was carried out in accordance with the method of example 1, except that the spindle speed in the spherical finish polishing was 150rpm, and the processing time of each step was as shown in table 3; the surface defect grade B of the sapphire spherical crystal obtained by spherical fine polishing for 40h is grade III, the surface-shaped diaphragm number N is 5, and the local diaphragm error delta N is 0.5.
In the embodiment, the local error delta N of the aperture is trimmed and slowed down due to the high rotating speed of the main shaft, and the local error delta N of the aperture is mainly trimmed by spherical surface finish polishing for 40 h; meanwhile, the surface defect grade of the sapphire spherical crystal is quickly improved due to the high rotating speed of the main shaft.
Example 4
The method is carried out according to the method of example 1, except that the diamond grain size of the polishing solution rough polished twice in step 13 is different from that of example 1, specifically, diamond with the grain size of 1-2.5 μm is selected, and the processing time of each procedure is shown in table 3; the surface shape f-number N of the sapphire spherical surface obtained after the spherical surface is roughly polished for one time is 5, and the local error delta N of the aperture is 0.86; the surface defect grade B of the sapphire spherical surface obtained after the secondary rough polishing of the spherical surface is more than VI grade, the surface shape diaphragm number N is 4, and the local error delta N of the diaphragm is 0.8; the surface defect grade B of the sapphire spherical crystal obtained by spherical fine polishing for 30h is grade IV, the surface shape diaphragm number N is 4, and the diaphragm local error delta N is 0.45.
In the embodiment, after two times of rough polishing, the surface defect grade B is more than VI grade, the local error delta N of the aperture is 0.8, and the surface defect grade B and the local error delta N of the aperture need to be improved by long-time fine polishing.
Example 5
The process was carried out in accordance with the method of example 1, except that the pendulum shaft pressure of 0.1MPa in the two rough throws in steps 14 to 15 was changed to 0.05MPa, and the processing time of each step is shown in Table 3; the surface shape f-number N of the sapphire spherical surface obtained after the spherical surface is roughly polished for one time is 6, and the local error delta N of the aperture is 0.9; the surface defect grade B of the sapphire spherical surface obtained after the secondary rough polishing of the spherical surface is more than VI grade, the surface shape diaphragm number N is 6, and the local error delta N of the diaphragm is 0.8; the surface defect grade B of the sapphire spherical crystal obtained by spherical fine polishing for 40h is grade IV, the surface shape diaphragm number N is 5, and the diaphragm local error delta N is 0.4.
In the embodiment, after two times of rough polishing, the surface defect grade B is more than VI grade, the local error delta N of the aperture is 0.8, and the surface defect grade B and the local error delta N of the aperture need to be improved by long-time fine polishing.
Comparative example 1
The process is carried out as described in example 1, except that two rough polishings are not used, but only one polishing is used; the corresponding process adjustment is as follows: step 14 is not performed, and step 15 is performed directly. The comparative example 1 directly carries out the secondary rough polishing of the spherical surface in the step 15 and uses the process parameters in the step 15, so that the spherical surface has scratch with the width of more than 0.1mm, the fine polishing removal amount is 0.01-0.03mm, the scratch cannot be removed, and the next procedure cannot be carried out.
Table 3: processing time of different processing stages in each example
| Working time | Milling and grinding machine | Coarse grinding of spherical surface | Spherical surface fine grinding | Once rough polishing of spherical surface | Spherical surface secondary rough polishing | Spherical surface fine polishing |
| Example 1 | 2h | 2h | 2h | 10min | 20min | 10h |
| Example 2 | Same as example 1 | Same as example 1 | Same as example 1 | 10min | 20min | 30h |
| Example 3 | Same as example 1 | Same as example 1 | Same as example 1 | Same as example 1 | Same as example 1 | 40h |
| Example 4 | Same as example 1 | Same as example 1 | Same as example 1 | 10min | 20min | 30h |
| Example 5 | Same as example 1 | Same as example 1 | Same as example 1 | 10min | 20min | 40h |
According to the embodiment and the comparative example, the indexes of the obtained sapphire spherical crystal, such as the surface defect grade, the surface shape diaphragm number, the diaphragm local error and the like, can meet the technical requirements or the national standard. Without the specific method of the invention, the scratches on the surface of the sapphire spherical crystal cannot be removed and the requirements cannot be met.
Furthermore, as can be seen from the embodiment 1 and the embodiments 2 to 5, the processing time can be further shortened on the basis that the quality of the sapphire spherical crystal finished product meets the requirement by adopting the preferable grinding tool scheme or the preferable spherical fine polishing scheme or the preferable coarse polishing scheme of the embodiment 1.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A preparation method of a sapphire spherical crystal comprises a sapphire crystal growth step and a sapphire crystal polishing and forming step, wherein the sapphire crystal growth step comprises the steps of loading, assembling a thermal field, heating, melting raw materials, adjusting liquid level temperature, seeding and growing, and is characterized in that,
the seeding and growing process comprises the following steps: putting the seed crystal down, touching the seed crystal with the liquid surface at a speed of 1.5-3mm/min, observing the weight change of the seed crystal through a weighing system after touching the liquid surface, adjusting the power of growth or melting and adjusting the rushing-in amount of argon introduced above to be 2-20L/min,until the weight of the seed crystal is kept stable, then the power is reduced after the seed crystal is stabilized for 1 to 3 hours, the crystal growth is started, the temperature is reduced after the crystal growth process is finished, and the dislocation density of the obtained sapphire single crystal is less than or equal to 1100ps/cm 2 The single crystallinity according to XRD test is less than or equal to 14 arcsec;
and the polishing and forming steps of the sapphire crystal comprise: s1, milling and grinding, S2, roughly grinding the spherical surface, S3, finely grinding the spherical surface, S4, roughly polishing the spherical surface for the first time, S5, roughly polishing the spherical surface for the second time, and S6, finely polishing the spherical surface.
2. The production method according to claim 1, wherein S2 the spherical rough grinding and S3 the spherical fine grinding each independently satisfy: the Brinell hardness of the adopted grinding tool is 100-270N/mm 2 The heat conductivity coefficient of the grinding tool is less than 45W/(m.K); the grain size of the adopted coarse grinding material is 90-110 mu m, and the grain size of the adopted fine grinding material is 20-30 mu m;
and/or the roughness Ra of the sapphire spherical surface obtained by the S2 spherical surface rough grinding process control is 1-1.2 μm, and the roughness Ra of the sapphire spherical surface obtained by the S3 spherical surface fine grinding process control is 0.25-0.35 μm.
3. The preparation method according to claim 1, wherein the spherical primary rough polishing of S4 and the spherical secondary rough polishing of S5 each independently satisfy: the Brinell hardness of the adopted rough polishing grinding tool is 35-50N/mm 2 The heat conductivity coefficient of the rough polishing grinding tool is more than 350W/(m.K), and a polishing solution containing rough polishing grinding materials is adopted, wherein the grain diameter of the rough polishing grinding materials is not more than 2.5 mu m.
4. The preparation method according to claim 3, wherein the rough polishing grinding tool comprises a concave spherical grinding tool for rough polishing of a convex surface of the sapphire sphere and a convex spherical grinding tool for rough polishing of a concave surface of the sapphire sphere, wherein a plurality of circular grooves and a plurality of vertical grooves are formed in the concave spherical surface of the concave spherical grinding tool and the convex spherical surface of the convex spherical grinding tool, the circular grooves are used for distributing polishing liquid, and the vertical grooves are used for introducing external air between the rough polishing grinding tool and the sapphire sphere; the circular grooves are arranged at intervals in a concentric ring mode by taking the center point of a concave spherical surface grinding tool or a convex spherical surface grinding tool as the center, and the vertical grooves penetrate through the circular grooves and are communicated with the circular grooves and are symmetrically distributed along the center point of the corresponding grinding tool.
5. The production method according to claim 4, wherein the annular grooves and the vertical grooves each independently have a groove width of 1 to 4mm and a groove depth of 1 to 6mm; and/or the groove width and the groove depth of the vertical groove are respectively larger than those of the circular ring groove.
6. The method of claim 4, wherein the sum of the areas of the grooves in the concave spherical grinding tool is 1/5-3/10 of the area of the concave spherical surface, and the sum of the areas of the grooves in the convex spherical grinding tool is 1/5-3/10 of the area of the convex spherical surface;
and/or a plurality of circular ring grooves are arranged at equal intervals, and a plurality of vertical grooves are arranged at equal intervals.
7. The preparation method according to any one of claims 1 to 6, wherein S4 the primary rough polishing of the spherical surface and S5 the secondary rough polishing of the spherical surface are both carried out on a grinding machine, the main shaft rotating speed and the pendulum shaft pendulum speed of the grinding machine in the secondary rough polishing of the spherical surface are both controlled to be higher than those of the primary rough polishing of the spherical surface, and the pendulum shaft pressures of the primary rough polishing of the spherical surface in S4 and the secondary rough polishing of the spherical surface in S5 are each independently 0.05 to 0.15MPa.
8. The preparation method of claim 7, wherein the process conditions of the first rough polishing of the spherical surface in S4 comprise: controlling the rotation speed of a main shaft to be 10-30rpm, the swing speed of a swing shaft to be 15-25rpm, and the pressure of the swing shaft to be 0.05-0.15MPa;
and/or S5, the process conditions of the secondary rough polishing of the spherical surface comprise: the rotation speed of the main shaft is controlled to be 30-50rpm, the swing speed of the swing shaft is controlled to be 20-40rpm, and the pressure of the swing shaft is controlled to be 0.05-0.15MPa.
9. The method according to claim 1,
s6, the spherical surface fine polishing meets the following requirements: adopting polishing solution containing fine polishing abrasive, wherein the grain diameter of the fine polishing abrasive is 500-1000nm;
and/or S6, performing spherical surface fine polishing on a polishing machine, wherein the process conditions comprise: the rotation speed of a main shaft of the polishing machine is controlled to be 50-150rpm, the swing speed of a swing shaft is controlled to be 20-40rpm, and the pressure of the swing shaft is controlled to be 0.05-0.15MPa.
10. The method of claim 1, further comprising: before the sapphire crystal polishing and shaping step, performing first segmentation on the bottom of the ingot obtained in the sapphire crystal growing step at a position 200-250mm above to obtain an upper first ingot; and performing second segmentation at the position 130-180mm above the bottom of the first ingot to obtain a second ingot below the first ingot, and taking the second ingot as a raw material for the sapphire crystal polishing and forming step.
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